Hydrogen Peroxide will increase contrast if added to a color developer. Speeds also shift so that the print must be rebalanced.

The Hydrogen Peroxide will rapdily decompose in your developer and lead to a pretty inactive developer in about 1 hour. There are patents on this by Kodak, Agfa, Konica and Fuji as well as patents on the use of Cobalt Hexammine Chloride which is slightly more stable but releases Ammonia in the developer causing fogging.

This is called RedOx Amplification.

It can also be used to cut the silver level during coating to obtain the normal contrast, thereby saving in coated silver in color print materials.