TwoCanoe,
For simplicity, I would use a dummy input like this:
#include <GUIConstantsEx.au3>
#include <EditConstants.au3>
Local $sMyHex = "0000FF"
$hGUI = GUICreate("Test", 500, 500)
$cInput = GUICtrlCreateInput(String($sMyHex), 10, 100, 100, 20, $ES_CENTER)
$cDummyInput = GUICtrlCreateInput(Dec($sMyHex), 110, 100, 20, 20)
$cUpDown = GUICtrlCreateUpdown($cDummyInput)
GUICtrlSetState($cDummyInput, $GUI_FOCUS)
GUISetState()
While 1
Switch GUIGetMsg()
Case $GUI_EVENT_CLOSE
Exit
Case $cDummyInput
GUICtrlSetData($cInput, Hex(Number(GUICtrlRead($cDummyInput)), 6))
EndSwitch
WEnd
Increase the width of the dummy input to see what is going on.
M23