pilpgam - thanks for the plugin suggestions but I might look into the code/event sheet suggestion by NetOne. The AdjustHSB plugin looked promising but it altered all the colours in the game as opposed to just colours on a specific level.
Tis not advanced very basic stuff
you really need lerp for a lot of things in games so good to understand
here I did background RED only on one slider to keep it simple so you can see how it works
the slider just moves value from 0 to 1 so result is it is setting red from 0 to 255
green and blue I left at 0 but if you clone 2 more sliders and put the same lerp then you can control all the colours
https://drive.google.com/open?id=1Rx7ysE4UydFQnvB0EmC2MWwFYY9G2FQb
NetOne - thanks for this.
I cloned the slider bar and called them SliderBarR, SliderBarG, and SliderBarB - then did:
System > Every Tick > System > Set layer 0 background color to rgb(lerp(0,255,SliderBarR.Value), 0, 0)
---------------------> System > Set layer 0 background color to rgb(0, lerp(0,255,SliderBarG.Value), 0)
---------------------> System > Set layer 0 background color to rgb(0, 0, lerp(0,255,SliderBarB.Value))
However, when I do this only the last slider bar in the event sheet works - in this case, SliderBarB. If I disable that then SliderBarG only works. Does this make sense?
Also, once I do get all 3 slider bars working together, I'm not sure how I'll automate it so it runs through a set selection of colour points.