Strange Color Difference

Can anybody come up with a logical explanation for the strip of stamps pictured below? I'm sure that the go-to answers will be sunlight or chemicals, but would like opinions anyway.

Several years ago, I purchased a group of PNCs that included the strip of 3 pictured below and it was received in the condition shown. While the two stamps on the right exhibit the normal colors for the stamp, the one stamp on the left is different. The yellow and red colors appear to be faded while the blue and green colors are not faded (they appear to be normal). Also, the text on the backing paper does not appear to be faded or different across the entire strip. The surface of the paper of the stamp does not appear to be any different on the left stamp than on the other two stamps.

Thanks,

Scott

Scott, nice strip.
Having said that, did you spot the plate number ? Could it be that the press ran out of ink ?
This is a good strip to show the folks at PNC3, and they may have a better explanation than I do


Peter

Perfectly consistent with the hundreds of previous threads here where the red end of the spectrum sun-fades before the blue & green end. It's always the red that goes missing first. I have no doubt this could be reproduced in month or two.

and the blue on the suspect stamp s somewhat faded

sure. it's all faded a little but the red, as expected, has faded the most

ya'll are one crazy group of posters on such an ultraviolet light altered specimen.
No one's mentioned the yellow is practically gone, but look you can still make out the petals. A paint that's lost its pigment to sunlight or fluorescent light, leaving the base (carrier) imprint behind. Red ink, not so delicate here as the yellow, as a tint is still there.
I think yellow is first to go for many issues. Like all the "F" for Flower (29c) tulip issues of 1991.