Bananas are yellow

A scientific study published in Na­ture Neu­ro­science in 2006 uncovered the interesting fact that our perception of colour is based both on the actual colour of the object and our knowledge on what it is suppose to look like, although this seems like an oxymoron as you would need to see an object before you know what it looks like.

Scientists have discovered "that co­l­or sen­sa­tions are not de­ter­mined by the in­com­ing sen­so­ry da­ta alone, but are sig­nif­i­cantly mo­d­u­lat­ed by high-lev­el vi­s­u­al me­m­o­ry,” that is, ex­pec­ta­tions.

This means that if we see a pure­ly black and white pic­ture of a ba­nan­a, it will look just a tad yel­low to us.