After using your U/A PCR Cloning Kit I can detect colonies, which are light blue, and not really white. Why is that?

Light blue colonies or blue colonies can sometimes be positive clones. If the LacZ alpha fragment and the cloned insert are in frame, LacZ complementation can occur resulting in blue colonies. Both white and light blue colonies on the same plate can result when the insert is cloned in either orientation and read through only occurs in one orientation. Incubating the plate overnight at 4°C will enhance the blue color facilitating the selection of white or light blue colonies.