H Rate Uncle Sam's Hat 3268 Color Error?

Hello,

Sorting through a box of kiloware, I found an interesting variety of the H Rate. I believe the Scott number is 3268. Uncle Sam's hat rim is aqua rather than gray. I can find no info on this variety. Is this an error? Is it rare? I am new to this forum and hope the attached picture works.

I am a novice collector of US stamps with on-stamp date and slogan cancels from the year of issue (not first day of issue, but rather stamps that served normal use through the mail). Anyway, I don't know much about errors or oddities. Help please.

They turn this color when exposed to light long enough.