In MS Paint you will probably get a colour like:
255 0 0 (Red) or
128 128 128 (Medium Grey)
To convert it into a Blockland format, divide each number by 255. Round it to about the nearest one or two decimal places.
1 0 0
0.5 0.5 0.5
The fourth number is the transparency - 1 is fully visible, 0 is completely invisible. If you want effects that you can see through or blended ones, use decimal numbers. For basic particles having 1 or 0.9 is better.
1 0 0 1
0.5 0.5 0.5 0.9