I have colored obj/geo nodes based on point geometry color using python . Now my point geometry color is animated . So how do I change color of a node frame by frame ?

You just ALT-Click on the word Color next to any color swatch. This will add a keyframe for that current color at the current time in the timeline. Change to a new frame and then pick a new color, then ALT-CLICK again to lock in that keyframe.

The numeric RGB color fields will turn GREEN to indicate there is a keyframe on them.