They seemed just as bright as the day they were done. Oils of mine from that period were already darkening with the overuse of linseed oil. I decided to give acrylics a serious try. They seemed sloppy and posterish at the beginning. There were other problems too like the color you put down was not the color you got.
Some pigments darken, others seem to lighten.
Then, without paying much attention to it acrylics started to win me over. I discovered that what I was losing on the straights I was making up on the corners. Hanging up oily canvasses and panels for days while running around in a Volkswagen bus in Europe was a pain. Acrylic canvasses come off stretchers and are easy to roll up and pop in the mail to the dealers. Work arrives across the puddle without a crack.