Overtone makes a sulfate and parben free clarifying shampoo called the Fader, I've never used it. There must be similar products from other brands. The efficacy depends on what kind of color is used and the condition of the hair.
If it's a very dark factory color, it's likely from a textile dye. I'll usually dissolve a teaspoon or two of Rit Color Remover in a small basin of water, microwave it for about 45 seconds, and swirl the hairpiece around in it for 30 seconds - a couple of minutes tops, checking the color very frequently. If necessary reheat the solution. This is not all that gentle, the more effective it is the more damage is done. But it should be ok to lift the color one level if it's just slightly too dark. This is probably the quickest and most effective method, but it's not for the faint of heart.
If it's hair color usually I'll do a deep conditioning treatment with a shower cap and apply heat from a blowdryer. That can be just as effective as clarifying shampoo, and obviously not as harsh on the hair. But with a lace piece I would worry about the integrity of your knots.
If you've got time, oxidation/sun exposure may be the safest bet, also damaging but there is no damage-free way to do this. It's a lesser evil kinda thing.
