Use 3mm. leds. ( like original nut bulbs )
If you use this type of leds (less than 20 mA ) , you must replace the 8 resistors .
Don't worry , it took me 3 days to find the right color
according my personal taste .
Anyway disconnect a VU and test the color inserting only one led .
Use a 1 kOhm resitor in series and external power supply with regulator ,
like a model train power pack .
Besides ,gently moving the led, you should find the reason of the shadow.
Ciao and have good job .
Marco