It's not that difficult. You can take the first measurement, then select the ticker on the first, do a second measurement to compare and click on the second ticker. You can see up to 8 graphs at the same time, plus the one u are measuring (in yellow).
I use the black background.
SpectraPLUS is very much customizable.
An alternative easier for SPL but without comparison is trueRTA.
SpectraPLUS is my favourite program btw.
Thanks for the reply, Telstar. Sory for not coming back to you in a short time, but work and reallife sometimes take my attention more than I would like to.
Anyway, I'll try to follow your advise, and will look to make a graph as similar as MikeC's.
Btw, even if a little bit late, Buon Ferragosto