>I'm going to make something like spells in my maps, so I decided to learn how to make at least existing spell working with cooldown. For example I have removed "RemoveObject" from fireball spell and now I need to make some cooldown, because if I don't do it, clonks will be able to cast fireballs without cooldown.

You could add an effect to the spell that wears off after time and doesn't allow the spell to be casted while it's on. Or you could save the last cast time and check if enough time has passed since that.

>Drawing maps

I think the question has already been answered here, still: The thing that matters with clonk maps is not the actual color, but the palette-index. mspaint is not really good at preserving it. You can draw maps in the console/editor mode of openclonk.