Just specify index this way:
{{ rgb |regex_findall_index(find='\d+',index=0)|int }}
Change index to 0,1,2 for each one like you are.
If you want to use the color picker, you’ll have to use the default hue/saturation passed in {{h}}, {{s}} and convert those to a color. I’d follow some other example, like: Using HSV / HSB to set colored lights