I have heard that adding red Kool-Aid powder will create a deepened red.
HTH
It does. I just posted two cakes with KoolAide frosting (in my photos). It works like a charm for red BUT it will give you a tangy Koolaide flavor so keep that in mind. 
For all the dark colors I add paste, mix, cover . I pull out a spoonful to let air get to it to see how dark it will turn, then if I need more paste then I add to it. Frosting DARKENS as it sits.
I always pre make......REDS, BLACKS, DK. GHREEN & BROWN.
You have to start making the red WAY in advance...look at my pics and you will see a 4 tier red cake. It took 2 weeks to get that much icing that red! Add some color, mix it up, let it set over night...eventually you will have the color you desire. Also, it darkens as it sets on the cake atleast 2 shades. Good luck.
BTW, now I use Americolor...much better than wilton color!
My most recent cake with the color red was the marine one in my pics. I used with wilton RED RED and Christmas red. It did take ALOT! I mix up my red first then start to frost the cake and do everything I can before I have to use the red. This gives it time to sit and deepen. Then if you're not happy with the color red, add more and keep adding until you achieve the red you are going for!
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