Whenever I dig up gladioli, the main bulb has at least a few baby corms. Perhaps when you leave them in place to overwinter, the main corm gets overtaken by one of the babies, and something in the mixed genetics might cause the offspring to have a different color. This seems more probable the more years you leave them in place - the original corm would gradually weaken, and one or more of the offspring wins out.
I haven't tracked whether they are different colors when I replant the baby corms separately. If I were trying for a single color, or color family, I'd be annoyed if they changed over time. But my bed of glads is multi-colored anyway. I'm just happy to see those lovely spears! And they're great as a cut flower, since a new bud opens every day or two. Just pull the wilted blossom, and trim the stalk if it gets too leggy for your vase.
Whenever I dig up gladioli, the main bulb has at least a few baby corms. Perhaps when you leave them in place to overwinter, the main corm gets overtaken by one of the babies, and something in the mixed genetics might cause the offspring to have a different color. This seems more probable the more years you leave them in place - the original corm would gradually weaken, and one or more of the offspring wins out.
I haven't tracked whether they are different colors when I replant the baby corms separately. If I were trying for a single color, or color family, I'd be annoyed if they changed over time. But my bed of glads is multi-colored anyway. I'm just happy to see those lovely spears! And they're great as a cut flower, since a new bud opens every day or two. Just pull the wilted blossom, and trim the stalk if it gets too leggy for your vase.