I'm never really here, thought I'd say hi and give you some flowers.
That's the beauty of it. If you want a consistent coloring on the petal, you just leave the stems in the water for the whole process. If you want a variety, you'd have to take them out after some time, then in again, then out, then in again.
I'd assume flowers have different configuration in their "sap" vessels, so the patterns would be different.
I personally like my flowers consistent, tbh.