dont put too much color in
I have used this before with one of the red Splat dyes.  Add the color dye a little at a time to the pastel.  The pastel doesn't put a big dent in the intense color so you have to go slow.  Remember, you can always add MORE!  I did save the color dye and used it again two or three months later.  I used duct tape to close it off.
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