I'm making a Star Wars costume with my daughter. I want to dye a white cotton/lycra unitard to be a chartreuse (yellow/green) color. Which of the Procion MX Dyes should I use to get this color? LemonYellow and Olive green? This is the dye color page:
http://www.pburch.net/dyeing/Store/JacquardProcionDyes.shtml
Here's the color I want to match:
http://www.lucasfan.com/interviews/oola04.jpg
Thanks.

I agree that a mixture of lemon yellow and olive green should give you approximately the correct color. This type of dye, Procion MX, is the best choice for a cotton/spandex unitard, because it can be applied in warm water (70°F to 90°F), which will not harm the Lycra at all. You will also need soda ash (also known as sodium carbonate), to set the dye.

There is more than one way to get a reasonably close copy of a particular color. The Jacquard Procion MX color mixing table suggests a large amount of lemon yellow and a tiny amount of medium blue (Jacquard Procion MX Medium Blue 072) to mimic the color of Chartreuse liquor. 

It is impossible to predict exact color results, but anything that is a slightly greenish yellow will probably work for that costume. I see some brown in the color on the page you sent the address to, as well. This would make olive green a good choice for mixing with the lemon yellow, because olive green contains a bit of brown.

If you want to be very precise in color matching, you must do some tests in advance, dyeing small swatches of cotton fabric. I confess that what I generally do for Halloween costumes is make my best guess and then go with it, without testing. Keep in mind that it is much easier to dye again to get a darker color, if you start out too light, than it is to remove excess color if you get it too dark.

For a perfect solid color, use the recipe for dyeing in a washing machine (though this requires a larger quantity of dye). For a slightly mottled or variegated appearance, let me recommend low water immersion dyeing, also known by the abbreviation LWI, as it is the easiest of all methods of dyeing, and the slightly mottled appearance can be ideal. For instructions, see How to Do Low Water Immersion Dyeing.

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