"Fast Mana" effects such as rituals are supposed to be in red's wheelhouse now, so why not stuff like this? It's always bothered me that the "Gold" mechanic in Theros was exclusive to black when they claimed they were moving the color away from that sort of thing; it's not like black got more Eldrazi Spawn than red during the original Zendikar.

And yes, there are no red Eldraz Scion making cards and 1 black one, but I never could follow the logic of giving so many Scion token-makers to blue anyways.

Hm. There's a flavor disconnect, though. Red has access to fast mana because it wants things now, Now, NOW! This can be seen as setting aside some mana for a rainy day... I could see this in just about any color but red.

To me, gold counters are somewhere between "fast mana" and "mana acceleration". This feels a bit odd in green, because you're spending a card to just get a one-off mana burst. But it also feels odd in red because you're saving it up. So it's probably ok in either, but I'm not certain.

A card that produced a variable amount of gold would feel a lot more red to me.

Scions in blue are apparently because blue gets to make colourless mana more than any other colour.

I agree this doesn't feel like red fast-mana because it's, well, slow. Although I don't think delayed mana acceleration has to feel nonred... How about:

Brewing Storm
Instant
Add to your mana pool.
Suspend 2 -

(That has problems with the mana arriving in your upkeep, of course. Needs either the Sakura-Tribe Springcaller rider or an "At the beginning of your main phase".)

Maybe this makes it more solidly Red then?