Robin:
Some S greggii form have developed the same way.Teresa and there are several other "Sports" that have developed this way.
Some of my neighbors on my street have followed my lead and
planted various Salvia's. One garden has had a solid pink
greggii this year one branch mutated and turned white with
pink streaks in it. Another plant Ruellia britoniana (3 foot tall)and has underground runners it developed a "witches broom".The resulting plant has the same color as the parent but smaller form ( less than 10") and comes true from seed.
Not to be out done it comes in 3 colors. Original was Ruellia b. "Katie"(lavender flowers) two pink forms 1)colobe pink 2) So Sue me pink and White Ruffles or Katie white" the only color the species does not come it is white.
Sorry about the novel... Salvias are amazing plants the forms of S.farinacea have the same ability.We had a "_Henryi Duelberg" throw a white with blue streaks in the lower lip
branch.
Lost the plant:( But as they say compost happens!
Keep us posted on seed!
Art
Art

I love the surprises! One of my cistus skanbergii threw a white sport this year. I meant to mark the branch and do cuttings and didn't get to it in time, of course. Of my seedlings from s. Shell Dancer, I've gotten light pink and a solid red so far. Waiting to see what the others turn out to be...nothing like going out to the garden every day to see what's 'new'.

I think I mentioned last year finding apparent coccinea x subrotunda hybrids. In that case the plants looked like coccinea but had red-orange subrotunda shaped flowers. I expect you are right about the value of your white flowered plants, the little subrotunda flowers probably do need a bright color - still, it is quite interesting.

Speaking of hybrids can you imagine my shock when this guy showed up in my garden. I thought it was supposed to be salvia greggii pink preference but on closer look realized it was not. The leaves are similar but variant in size as the following shots reveal. I have nicknamed this thing "white throat". It is also a bit larger than some greggii at 32".

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I'd love to see an image of Salvia madrensis x gesneriiflora.when it becomes available. Madrensis is totally hardy here in North Carolina.