To me contast does not have to be glaring,but when I was hosting a block lotto,a lot of blocks came to me that were little to no contrast and they stood out like a sore thumb.For example,a Bears Paw in a very light pink with a white background.It looked pretty up close,but always stand at distance and look. The pattern totally dis appeared,and did not fit in with the rest of the blocks at all.This is a common mistake with newbies.I love pastels,but seldom work with them with a pattern,I save them for larger squares or such.Its a lot of work to make a pieced block and then it disappears into the background.The more intricate a pattern is,the more contrast you need,and that includes scale and color.Hope that helps.