I assume you are using LC's colors. Just take the red cap off, poke a hole into the spout at the top so that the color can get out(do not cut the top with a knife) and then you can put the red cap back on after you get the required number of drops out.
You do this for each and every bottle of color you have. Do not move the red cap from one color bottle to another. When you are applying the color to the plastic only un-cap one bottle at a time, that way there will be no mixup.
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