This effect will allow you to change the colour of the rubber stamps in a particular sequence.
Just like you did with the levels, go to the Effects Window and choose :
- Video Effects > Colour Correction > Colour Balance (HLS).
Drag that effect onto the footage in the Timeline.
Referring to the Effects Controls and the Colour Balance settings, you can then adjust the Hue (which means, shift the attention of the inherent colour range in the pixels). Adjusting the Lightness reduces the amount of light and makes the selection darker, or, moving the slider the other way, shifts the lightness towards full brightness.
Changing the Saturation adjusts the purity of the colour (or adds complementary values and desaturates the colour).