third eyelids showing a little - something to worry about?

[ZeroCat]

My two-year-old cat is getting over a cold and we've been giving him l-lysine powder as per our vet's instructions. I'm growing a little concerned though as his third eyelids are showing a wee bit in each eye (1/8"?) - not a whole lot, but enough for me to notice that something's not quite right. I'm wondering if this is normal - for the third eyelid to show a bit when a cat has a cold. I'm willing to monitor it for a few days... but how long should I wait before returning to the vet? Any natural remedies anyone would suggest?

Thanks in advance for your help!

=^..^=