They will see red only. So white light minus blue and minus green is red. Also white light minus green and minus red is blue. But red and green together is yellow, so white minus yellow is blue. This is just the reverse of what we said above, white minus blue makes yellow.
Color works both ways.
These other colors are known as complementary colors since they add to produce white. Y. Move your hand closer still and notice that a classic black shadow appears in the middle. Where your body blocks all three lights, no light reaches the screen. Put an eye in the shadow, it will see no lights. White minus red, minus green, minus blue is black.