I know how to apply the fill pattern but how to change the color of the pattern? Is there a way to do this?
If you’re using the Fill tool, it’s limited to filling with patterns ‘as they are’ from the Patterns docker. You can create your own patterns as .png files with any colour you like and transparency and put them in your personal resources folder. They will show in the Patterns docker when you start krita. However, it is difficult to make complicated patterns that tile well.
The quickest and easiest solution for you would be to apply the pattern to a brush preset and paint the pattern onto a selected region. That way you could have the pattern any colour you like.
Select a simple solid brush such as ‘b) Basic-2 Opacity’ and open the Brush Editor (an icon on the toolbar) then click inside the checkbox for the Pattern item in the left side list of properties. The Texture (pattern) tab will be shown and you can select a pattern. The Options tab will let you adjust the Scale of the pattern, among other things. Then click outside the brush editor to close it and you’ll have a brush that paints coloured patterns.