Can you cast a spell with alternative cost using mana from a Selvala, Heart of the Wilds tap ability in a Commander game?

Selvala, Heart of the Wilds has a tap ability that adds mana in an amount equal to the greatest power among creatures on the battlefield, producing green mana (or sometimes colorless). This mana goes into your mana pool just like any other mana and can be spent on anything you could normally spend mana on, including alternative costs (CR 117.9).

Alternative costs are simply different total costs you may pay instead of a spell's mana cost (CR 118.9). Common examples include Overload, Surge, Flashback with a different cost, or cards like Force of Will's alternate cost. As long as the mana Selvala produces satisfies the color and amount requirements of that alternative cost, you may use it freely. Mana itself has no memory of its source once it is in your pool (CR 106.4).

The one important restriction is the Commander color identity rule (CR 903.5d): you can only include cards in your deck whose color identity fits within your Commander's identity. If your Commander includes Selvala (green), you cannot run Force of Will (blue) in the same deck anyway, so the alternative cost paying a blue pip would be moot. Within a legal deck, there is no special restriction on using Selvala's mana for alternative costs.

Example: You control Selvala and a 6-power Ghalta, Primal Hunger. You tap Selvala to add {G}{G}{G}{G}{G}{G} to your mana pool. You then cast Runic Repetition using its regular cost, or cast any green spell with an alternative cost like Overload on Cyclone Summoner (if your Commander were blue-green). The mana works perfectly for any legal alternative cost you can pay.

In short, mana from Selvala's tap ability is completely normal mana and faces no special restrictions when paying alternative costs. Just ensure the colors match and the cards are legal in your Commander deck (CR 106.4, 117.9, 118.9).