The color of the easel surface definitely makes a difference! You can test this yourself. Figure out what exposure you need to create a medium gray on your paper. Prior to making this exposure, mark the back of the print with a thick black felt-tip pen. Write a number on it or sign it. Then make the exposure and process normally. You should not be able to see your mark on the emulsion side after drying.
Whilst you can see the difference between reflected light using black and white easels, I suspect that the difference between yellow and white would be much smaller as a yellow surface will still reflect a fair amount of blue and green light.