You can pick colors using JQuery Palette Color Picker
form do |f|
f.inputs "Details" do
f.input :color, as: :color_picker
end
f.actions
palette
: If you don't want default, you can pass your own colors:
form do |f|
f.inputs "Details" do
f.input :color, as: :color_picker, palette: ["#DD2900","#D94000","#D55500","#D26A00","#CE7D00","#CA9000","#C6A300","#C2B400","#B9BF00"]
end
f.actions