There's some great answers to your question below, but I'll add mine anyway. Because of the way our eyes see blue (as highlighted in the OP), and especially Yve

There's some great answers to your question below, but I'll add mine anyway. Because of the way our eyes see blue (as highlighted in the OP), and especially Yves Klein blue, it has some slightly magical properties in art. The flat blue canvases are absolutely uninspiring at first glance, but stand in front of it for 30 seconds and it starts to recede - it becomes hard to tell how far away the canvas actually is. You're unable to make out texture on the surface because the brain is struggling to actually work it out. It's most striking on the sculptures though, they almost entirely lose their depth and become a flat thing that changes shape as you moved around it. Imagine a 3d rendering of a gallery scene where there's one model that is untextured and unlit - it's like a brilliant blue silhouette. I took my then 5 year old daughter to the Tate for the exhibition and it had the same effect on her, while almost everything else on show had no effect at all. The only other thing she loved was Bridget Riley, and I think Yves Klein's blue work is somewhere in the same realm - the art is in defining something that makes the viewer's brain do some of the work, that is going to be experienced slightly differently by everyone who sees it.