This is going to be tricky and you need the XML-editor for this.
1. copy or notice the hex value for the color you want to apply
2. open XML editor and select the pattern filled object
3. under "style" you´ll find an entry like "#pattern1234"
4. look up in svg:defs something that matches the description: "pattern1234" and it´s core description "pattern id=pattern1234" and its content: like <svg:rect id="rect1234"
this last entry will contain the style fill:#.......;stroke none - here you exchange the value behind "#" and a "return" will make change the color value.
Beginners' Questions How do I change color pattern fill?
Inkscape.org
In the fill and stroke area how do I choose the color??
Even after I change the fill color it does not change?
If I select a different color it deletes the pattern
This is going to be tricky and you need the XML-editor for this.
1. copy or notice the hex value for the color you want to apply
2. open XML editor and select the pattern filled object
3. under "style" you´ll find an entry like "#pattern1234"
4. look up in svg:defs something that matches the description: "pattern1234" and it´s core description "pattern id=pattern1234" and its content: like <svg:rect id="rect1234"
this last entry will contain the style fill:#.......;stroke none - here you exchange the value behind "#" and a "return" will make change the color value.
I´d say it´s much easier to make a new pattern by going Object->Pattern->Objects to Pattern.