I like SEM dye. I used it on my 78 back in 08 or 09 when i restored it and it's still holding up like new, 10 years and 50,000 miles later.
As far as what color to buy, Call them and ask them. Then go off their advice and buy the color they recommend. DO NOT use it on your actual panels, test it out on a scrap piece of whatever, to see the actual color. If it's wrong try again, and don't try to match the new paint to your old faded parts. The new paint even if a perfect match for Stock original may not match the colors you have now due to fading.
It's a trail and error thing. But I can vouch for SEM products working wonderfully as long as you follow their instructions to the tee. buy all the other products they recommend to go with it and do as they say and I can vouch it will last 10 years/50k miles with heavy dirty use to it. It just wipes clean like the OE plastic used to.