Java Edition:Soul Fire on Non-Soul Block
Usually, when fire generates or is lit onto a non-soul block, the fire's color is red, though a few methods allow you to get the blue soul fire on a non-soul block.
Obtaining
needs info on MC-170954
Update Suppression
It is possible to create this illegal fire combination via update suppression.[test]
23w13a_or_b's less_interaction_updates Vote
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Using the less_interaction_updates vote in snapshot 23w13a_or_b, placing down a block of soul sand/soul soul, lighting it on fire, and then breaking and replacing the block below it with a non-soul block allows for this discontinued combination.