Source for Lionel Lines colored paint & decals

 The biggest problem you will have is that the colors can be different on the Lionel livery items.  I may be able to help you with the orange though.

 

I just added ditch lights to my LL Alco C-420.  It was released close to the same time as your GP20.  I was prepared to try and color match the orange.  When I went in my paint drawer, I pulled out several bottles of Floquil.  The Floquil SP Daylight Red looked close...after shaking it, it looked VERY close.  I coated the brass ditch light housings with gray primer.  The next day I brushed them with the Daylight Red...PERFECT MATCH.

 

Hopefully this will work well for you.  I assume you're going to airbrush...the color may change a little when mixed with thinner.  For my little housings I just painted straight from the bottle with brush...no thinner.  You may want to test it out on scrap plastic first.

 

 

 

Floquil CSX Blue might be a good start, when trying to match the Lionel blue.

Thanks CandO.  I'll be brush painting.  Will test out first.   I've got the LL Alco C420 from the SS set and the upgrade boards bought.  Should be here any day.  I assume your's is upgraded to TMCC-how are those Alco sounds

I also have the LL 1997 GP9-that's a beauty-great runner and cool horn

Prima donna-not happy with an orange tail and an all blue nose.  Go figure...

I am hooked on Lionel livery items. That GP20 will look great with an orange nose. I don't have one, but I have Centennial GP9. The GP9 gets a lot of run time...great runner. I just got the C-420 recently and I have not purchased the upgrade boards. I searched online, but couldn't find the command upgrade board. I did find the RailSounds upgrade board listed though.

I can hook you up with the boards.  I insisted on getting an Alco C420 sound board because I had a LV C420 that I traded for a set and it had the coolest sounds ever.  Knocking and clanking-there's nothing like it.  You don't want to get a generic diesel board or you'll miss out on the true Alco sounds.  I missed having one so I jumped on the sale of the SS set.  Why it's not here yet is another story.  Both the set and the upgrade boards should be here soon.  I also ordered electrocouplers for the GP20 & GP9 to upgrade them.  I am interested in this and figured these projects are a good start.  I'll keep you posted.  Here's the new (to me) queen of the rails 

Just thought I'd post a pic of my LL steam fleet.  # 2000 is giving me the silent treatment right now.  I think I need a new sound board, which is ok because it's identical to another steamer I have.  Great runner though, I'll get her back.  The # 773 is part of PWC series set and is awesome.  Great whistle, great runner, just the epitome of what I like-simple elegance.  Cheers