This kind of situation is mainly caused by eye infection. Generally speaking, conjunctival blood vessels are in the ''sleeping'' condition and does not have blood through them. So the sclera is white, but once suffered invasion by bacteria and virus, the "sleeping" blood vessels will soon be ''wake up'', then expand. So red blood flows to the eye, and sclera become red. I suggest you continued to cure your cold, you can use some anti inflammatory and take more vitamin C. At the same time, you should use some eye drops prevent conjunctival infection.