I work in early childhood in the 2-3.5yr old room and I think your childs development of colours sounds fine. The range of skills that a 2yr old has vary so much that it is definatley within the 'normal' range. I usually tell parents to work on one colour at a time so that their child doesn't get confused. For example go on a red colour walk (pointing out everything red around the house) every day for a week or until this colour becomes concrete then move on to the next. Depending on your child's language development at the end of each walk you could ask them to label the colour but for a 2yr old I would just initially be saying "can you go and find me the red car etc" rather then "what's that colour " all the time as that can hurt their confidence. We would normally expect children to know all primary colours by around 3yrs. Hope this helps.