I planted cucumber plants a week ago and now the leaves are turning white. Is this normal?

It could be what they call "chilling injury (http://64.233.167.104/search?q=cache:nLQwMWSgSQAJ:countyext.okstate.edu/carter/Backyard%2520May%252014.pdf+cucumber+white+leaves&hl=en&gl=us&ct=clnk&cd=8)".

"temperatures in the 40s and low 50s can cause chilling injury."

Does that article help?

I also found that there are diseases that result in the leaves having white "stuff" on them, but it sounds like you're saying the leaves themselves are white - so probably not disease from what I could find.