Posted By:
DavidTrevor. I don't closely follow the T205s, but I am assuming from your description that the one on the right (yellow background) is the normal one.
Color variations are cause by variations in the amount of ink applied during printing. For example, yellow ink followed by red ink will produce orange. During mass production it is common for some slight variances in the amount of ink added to the printing plate. For example, due to the change in yellow or red inks, a card will appear a darker orange at one point and lighter at another. Even you you look at Topps cards from the 1970s and 80s, you will see that slight variations are normal ... The typical bizarre variations are when one color is either barely added or not at all added-- thus a red or yellow card.
If your card is ordinarilly yellow, then it would seem that the printers for some strange reason added an extra and unintended color. But, as I noted, someone else can better comment on the rarity of your particular color variation.