Greg7579
Forum Pro
That is true but auto WB has improved greatly. Plus, you can do with temp whatever you want in post.I've never seen an AWB algorithm that works anywhere near as well as WB to a gray card.
Not many people walk around with a gray card, but yes, if he is being deliberate with the flowers there is nothing hard about placing a card in the scene for a test shot in order to hit it with the temp dropper in LR in post later (or set a custom WB for that scene).
By the way, I know what a gray card looks like, so I sometimes find a portion of the scene that looks like the color of a gray card and hit it with the dropper in LR.