Color matching with decals is a painful experience for me. I can never get it right. More "trial and error" - the only way to learn. Keep up the good work.
You can purchase colour charts
http://www.pantone.com/pages/pantone/pantone.aspx?ca=1 but i dont know how good they are. you would need a fairly good printer thats calibrated well. but really you should use a well calibrated printer anyway! but I dont because you can get a $20 printer from anywhere! (mine was from local post office!) but its the Ink that costs (you need to have goood quality ink that sometimes needs a dearer printer but also refilling cartriges can make the cartridge loose calibration)
I don't worry too much. a printer that has good for photo printing attached to it is good enough for me. Its getting photoshop thats a main hassle!
http://www.adobe.com/products/photoshop/photoshop/whatisphotoshop/ well look at that link, for just photoshop (the basic up to date) from US$699! That is adobe Photoshop CS5.1.0, I use Adobe Photoshop CS1.8.0! Thats why it takes me a while to do the photoshopping (a lot less tools and options but still possible just time consuming) I have used Adobe Photoshop CS3.10.0 bu cant get my hands on anything newer with out losing $ out my pocket. It's something i'll need to just live with for a while, oh and the newest full adobe package is
http://www.adobe.com/products/creativesuite/mastercollection/ I think you would need to work for them to get a discount to afford it! US$2,599 a pinball itself! keep in mind when you buy photoshop i think you get 3 or 5 licences (i'm not sure how many) but if you can understand it and do playfield restorations or backglass restorations or any large printing it's worth getting a big printer (possibly uv) and investing in photoshop!
