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Colour blocking is one of three techniques for sewing multi-colour suits.

The most common question I get about colour blocking is 'How do I make a red and blue Spiderman costume?' Spiderman is owned in various exciting ways by Marvel Comics, who I imagine are as depressingly litigious as most other American companies, so I'll be referring to Cobwoman, to the side here, who gained her mysterious maize-related superpowers in a gruesome combine-harvester accident which deprived her of her head. She still leads a happy and fulfilling life though, so don't feel too badly for her. (In passing, the black and white 'Venom' Spiderman costume is obviously a candidate for a white appliqué spider patch on a black suit, but don't tell Marvel I told you.)

Before I start properly, note that it's usually better to make a 90% accurate costume that's within your abilities than try for a 100% costume which is a bit too complex. Costumes are more about the performance than the looks, and the advice I see time and again about them is 'exaggerate your actions.' Most folks will recognise the intent behind a costume without worrying that 'the real one has seven stripes, not five', or whatever.


Colour blocking involves cutting the pattern along the line where you want the colour to change, then adding a seam allowance to both sides, in order that when you sew the resulting pieces of fabric together, the final piece is the same size and shape as the original pattern piece. It is best suited to simple bold designs, because intricate colour blocking would result in far more seam than any self-respecting superhero would want in her slinky skin-tight supersuit. (Why do you think the webbing on Spiderman's costume is usually made with a laundry marker or that strange fabric paint which forms strands on the surface, rather than being sewn-in piping?)

Which base pattern you choose depends on the nature of the pattern you're adding - if there's a symmetry in a seam line which some particular pattern has, it makes sense to take advantage of that. Most superhero costumes seem not to have a centre front chest seam though, so single panel is normally right for the top, but many superheros have a colour-transition at the waist, so you could switch to a conventional two-panel leggings pattern below. Superheroes who forget to wear their underpants on the inside are probably best represented with the leotard style in-set legs.

Colour blocking makes order of construction important because sewing around sharp angles is extremely difficult. For instance, where the diagonal sash across Cobwoman's chest meets the waistband, you won't be able to sew that sharp angle, so you will need to do one of two things:
Either continue the diagonal as a piece - in this case, you will sew the yellow triangle to the green waistband first, and then sew that piece to the green sash.
or stop it at the waistband - in this case, you will sew the green sash to the yellow triangle, and then sew that piece to the green waistband.

Which of the two alternatives you choose depends on the precise nature of the costume and the natural flow of line. For Cobwoman above, I'd probably use the second option, because the waistband is quite strong and the sash isn't disrupted by being cut off. It also matches the way the inside arm panel will obviously be cut off by the gauntlet as shown to the left here, (rather than the inside arm panel extending into the gauntlet and... presumably down to the fingers, which would only make sense if the two colours went all the way to the fingertips).

For Cobwoman's rather fetching Nacho Extreme outfit to the side here, where there's a vertical chest panel leading into a waistband, with panels to either side, to pluck a completely arbitrary example from the air, the strong lines of the side panels would make me go for the first option so the the chest panel cuts through the waist band (the vertical cuts marking the panels are continued into the waistband) and sweeps right down to meet with the leggings below. In that case, the order of sewing would be: panels' bottom border to waistband, sides to chest panel, then leggings to the top.

Note: It's important that you avoid the temptation to turn the bits of cloth through odd angles to save fabric: don't cut the green sash along the edge, cut it diagonally. Pretend that your costume is to be made from velvet, and you want all the velvet to 'stroke' in the same direction. If you don't follow this advice, the different bits of cloth will stretch in different ways, and you'll end up with puckers (and all the supervillans will laugh at you).

Note: If you can, avoid colour blocking along a curve - it's much trickier aligning the inside and outside of a curve so they sew together without bunching or wrinkling than aligning a simple straight line, and you have to do clever things like cutting notches or slits through the seam allowance just enough to stop wrinkles but not so much that you get gaps in the final seam. If you really have to block along a curve, you might find it easier to use a technique more like applique below, with the two pieces' right sides facing the same way, and the seam allowance for the topmost folded under. Failing that, use lots of pins, lots of care, and lots of time.

Be aware that certain patterns are virtually impossible (or at least very fiddly) with blocking; you may need to resort to cheating with a combination of blocking and appliqué. For instance, these look similar, but the first is challenging:

Other techniques

The other techniques:
the relatively simple process of stitching a shape onto another piece. It takes time and patience and lots of pinning, but is relatively easy: sew it while the pattern pieces involved are still flat, rather than after you've mostly assembled the suit, and use zig-zag along the edge.
the fiddly process of sewing a fold of contrasting colour into a seam so it protrudes visibly. You can buy piping with a string inside to keep it standing proud, but it's never stretchy, so use a strip of lycra if you want it stretchy (you can just cut this strip parallel to the selvedge - don't worry about the 'cut it diagonal' advice above for this particular case). It's probably easiest if you sew the piping to the pattern piece on one side of the seam, and then sew the other pattern piece on.

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