This is a photoshop-like (simplified) HSV colorpicker window.
I know similar stuff has been made in dxscoreboard resource, but i always wanted a standalone colopicker.

This resource provides 2 exported functions:

exports.cpicker:openPicker(id, color, title)
returns true if picker was created successfully
or false if a picker for that ID is already open.

arguments:
id - element/string/whatever - stuff that will be returned in event for you to know for which element the picker was opened
color - optional, if set to hex color, will open picker with that color selected
title - optional, sets picker window title

exports.cpicker:closePicker(id)
closes the corresponding colorpicker window (same as "Cancel" button)
returns true if picker for supplied ID existed,
false otherwise

------

when "OK" pressed in picker, it triggers a client-side event "onColorPickerOK":

example usage:
-- simple editbox
local edit = guiCreateEdit(0, 0, 0.1, 0.05, "", true)

addEventHandler("onClientGUIDoubleClick", edit,
function()
-- adding a handler, so when editbox double-clicked, it'll open a colorpicker window:
exports.cpicker:openPicker(source, "#FFAA00", "Pick a color for some editbox:")
end)

-- this will be triggered when "OK" is pressed in colorpicker
addEventHandler("onColorPickerOK", root,
function(element, hex, r, g, b)
-- the following arguments are passed in the event:
-- element - contains whatever you passed when opened the picker
-- hex - hex code of picked color (in the form of "#RRGGBB")
-- r,g,b - r,g,b values of picked color
--
guiSetText(element, hex) -- set the picked hex value to the editbox
end)

---

UPDATE: "onColorPickerChange" event:
the same arguments passed to this event as "onColorPickerOK", example usage:

addEventHandler("onColorPickerChange", root,
function(element, hex, r, g, b)
-- assuming you've passed the vehicle element when opening colorpicker:
setVehicleColor(element, r, g, b)
end)