If you know how to get the weather data that you want and are able to do something with it outside of Rule Machine, and if the subset of possible weather condition states is reasonably small, you may be able to do something with virtual switches.
e.g. If you know that you have 16 possible weather states (sunny, partly sunny, mostly sunny, cloudy, partly cloudy, mostly cloudy, clear (night), raining, sleeting, snowing, hailing, foggy, windy, t-storms, showers, other?), you could create 16 virtual switches, and name them accordingly for the naming convention in your HA environment.
This grouping of virtual switches will act as an input mechanism for getting weather data inside of Rule Machine. When the state changes, turn the virtual switch for the associated state to ON.
Then, configure rules in Rule Machine to monitor the ON/OFF state of the virtual switches (i.e. Rule Machine doesn’t care that the switch is just a switch. You, the user, know what state each virtual switch represents, and you’re the one making the rules), and do things based on those switch ON/OFF states; like your light bulb color changing scenario.
I know it leads to having bunches of virtual switches in your device list (especially if you use this same technique for other types of automations), but so what?
Pay no attention to the man behind the curtain.
p.s. I assume the moment I post this, somebody will probably show why my idea sucks and will give us a real solution, but in the meantime, I think this is at least feasible.