I wouldn't recommend automotive coolants, they also don't smell that good. But some can be used. Regarding coloring, I use regular distilled without dye. Too many of the boutique watercooling dyes break down after a year for me to bother with them, others have ingredients that wear out the pump faster. But Pond Blue coloring also works rather well as it doesn't break down, but I'm not sure if you can find the same stuff over there. Don't use pool dyes, those break down within a couple months. 
 
To change the fluid be sure to do a full system flush. Some recommend vinegar if you need to remove old dyes or buildup. If you use distilled water be sure to add a biocide, personally I use pond algaecide as that stuff inhibits bacteria and algae both for an extremely long time. 

We only use distilled H20. Nothing else. Ain't nobody got time fo dat colored gunk coolant 😎

I recommend distilled water. I tried a red pastel coolant which ended up staining all the tubing pink and ended up replacing after about a year when cleaning.

distilled water with ptnuke is what I use plus its cheap for a 1 gallon jug.

When I was running custom loops I used distilled water with PT Nuke biocide.