The influence of colours and contrasts

Obstacles can be easier or more difficult to jump depending on use of colours and contrasts.
Here are some examples:

No.1 The poles are totally white and without any contrasts which makes this obstacle most difficult of this four examples.

No.2 Nearly the same difficultnes but the black lines on the poles makes it little easier to jump for the horses.

No.3 The red painted parts on the white poles makes this obstacle much easier than examples No.1 and 2.

No.4 This is the easiest obstacle of them all because of clear contrast between red and white.