Why can a bright orange area become an effective focal point within a dark blue field?

Correct answer: Because of complementary colours and value contrast

The governing concept is emphasis created through contrast. Orange and blue are complementary colours, so their opposing hues immediately separate the orange area from the blue field. If the orange is also brighter or lighter, value contrast adds another attention cue. Therefore option A is correct; shape similarity, absent lines, and equal colour temperature would not by themselves establish a strong focal point.