OK just put brain into gear
Use high side switching (FET or transistor) but with current control resistors on high side of LED (LED cathodes connected to ground)
The arduino inputs now look directly at voltage on the LED anodes.
This will vary from 0volts (LED off) to somewhere between 1.2 and 3volts (depends on LED characteristic) for LED on.
That way you do not need any potential dividers.