For thin-film interference, remember the relationship: thickness is proportional to the wavelength for constructive interference ((t propto lambda)).
Thinning film (like a dying bubble): Color sequence shifts from red (to) yellow (to) blue (to) black (destructive interference for all wavelengths).
Thickening film (like a newly formed bubble settling): Color sequence shifts from blue (to) green (to) yellow (to) red.
The question describes a bubble thinning over time, so the color shift is towards red, but eventually all colors disappear starting from blue.