One of the benefits of having a stamped concrete patio is that you can add color to your cement. Most contractors apply color hardeners to your stamped concrete patio using a "dry shake" (similar to a powder) color hardener.
Once a Color Hardener Has Been Added, Can It Be Removed?
Because color hardener is applied to fresh concrete then dried using the traditional drying methods, removing a color hardener from your stamped concrete patio is almost impossible and may require additional expense.
In some cases, if you wish to remove the color hardener prior to it setting, you can use a pressure washer set at about 3000 psi and wash out the color. Keep in mind however, that by doing so, you run the risk of also washing away some of the cement which could result in weaker or compromised surfaces once the cement cures.
You can also use chemicals to remove the color hardener. Check at your local home improvement store for a chemical stripper that is designed to be used on concrete surfaces. Using a chemical not designed for that use may result in damage to your stamped concrete patio.
Contact the contractor that laid your stamped concrete patio as well, he will be able to guide you should you decide to remove the color hardener. It is typically not recommended, however.