I agree the RUG list should be in the primer. JBinder, you've had great results and that looks like a strong list! AngryBacon was on RUG too.
Over the last week I'm at 16-3 with UWR.
I've swapped around a few SB and protection slots in between, but have kept roughly the same manabase and core. I haven't had color problems with this.
I went up to 17 lands for some of those games (with a 2nd Volcanic Island) then cut it for
Preordain #3.
I've never had much problem with color access, though sequencing cantrips and fetches in the first few turns is really important. I noticed in testing and goldfishing that fetching the wrong land at the wrong time or using the wrong fetch first can screw you out of a color. I cantrip and fetch more carefully than I would playing something like Delver. Lotus Petal is also a great way to get the red for Breach when you just have Islands and Plains out.
Lemon, you have 2 colorless lands in a 3 color deck. I wonder if they make a difference. How often do you activate Hall of Heliod's Generosity?
Another option is to forget the basics and go heavier on duals like a 3-color Delver manabase:
4
Scalding Tarn4
Flooded Strand3
Volcanic Island3
Tundra1
Island
It's tried tested and true, you just have to accept you'll get Wasted sometimes. I had very consistent colored mana with that in the early test shells (50+ goldfishes, 20ish test matches vs Delver). Unless Delver double Wasted me early with a clock, being vulnerable to Wasteland wasn't that big a deal. You have cantrips and backup copies of duals. Delver decks have been pulling it off for a while. Most storm decks are dual-centric. 3 color manabases do work, with the right support. It's a calculated decision whether you think you'll have to face multiple Wastelands more often than you'll gain wins from easier access to colors.
I'm surprised URW lost to the UR mirror 0-2.
Silence wrecks the mirror. Why do you mulligan so much? Was it just bad luck with really awful hands, or are you trying to mull into the combo? We don't need to. Fetches, cantrips and some interaction (FoW, Silence) could be enough to keep 7. Check out AnziD's stream. In some matches we can play the control role. It's not always a race.
Good luck with the 2 color build!