17 months is still pretty young my dear. don't worry about it. just keep repeating the color to them. don't go into sorting yet. getting them to know the color is important. other then using color blocks. use daily life items as an example. Blue taxi, red car etc. just show them the different colours daily. Soon without realising, they actually know the colours well!
Still too early! it's a bonus if your child is able to know the colors at such young age. Every kid is different. Just guide them daily on the different colors available in the world. Just point to them and say the colors.