The Randomize function modifies the color of isolated areas (i.e. the bricks here) on the texture.

Use the Tolerance value to set the limit of allowed color deviation, which is still interpreted as one, single colored area.

What color channels should be modified, can be controlled at the HSV Channels panel. The hue and brightness channels were changed to get Image 2.

The strength of the color modification is regulated with the Amplify value. Small values (<30%) are sufficient for most purposes.