\definefontfeature[arabic][arabic][goodies=amiri, colorscheme=default]

\definecolor[colorscheme:1:1][r=1]
\definecolor[colorscheme:1:2][g=1]
\definecolor[colorscheme:1:3][b=1]

\definecolor[colorscheme:2:1][c=.55]
\definecolor[colorscheme:2:2][m=.55]
\definecolor[colorscheme:2:3][y=.55]

\setupalign[r2l]

\starttext
\definedfont[name:amiri*arabic at 36pt]
\setfontcolorscheme[1]
ضَرَبَ ضُرِبَ ضَرْبًا

\setfontcolorscheme[2]
ضَرَبَ ضُرِبَ ضَرْبًا
\stoptext