What would an american flag look like if you viewed it through a filter that transmits only red light? what would it look like through a filter that transmits only blue light?

The US flag has 3 colours, blue, red and white.

Now, first you need to remember that the white is a combination of all the colours, and black is the absense of all colours.

Only red lights:

The red in the flag is transmited, because the filter does not affect that colour.

The blue is absorved, so the blue parts will turn black

The white light is all absorved exept for the red contribution, so the white parts are red now.

Only blue light:

Simillar to before.

The blue parts are not affected.

The red parts are black now.

The white parts are blue now.