RGB as well as TGE's 1.000 = 100%, so 0.500 0.500 0.500 would be grey and 1.000 0.000 0.000 would be 100% red.
A way to find colours is opening paint then double click on any of the colours in the top bar then hit Define Custom Colours, click on the panel on the side until you get a colour you like then write down the RGB number and try it in Blockland.