Her Wikia page says this about the colors of the speech bubbles:
Todd Klein, the series' letterer, draws her speech as a scrawl, against a multi-colored background, sometimes the background color will match the mood she is in (red for anger, blue and green for calm, etc.).
They don't, as far as I can tell, have a citation for this claim. It appears to be copied almost word-for-word from Wikipedia, which doesn't source this claim either.
I can't analyze Delirium's utterances in other works (and searching the web for pictures shows that the colors are used somewhat differently from the way they're used in Season of Mists, with more colors and waves of colors per bubble), but I see that Delirium speaks in only thirteen panels in this issue (pages 8-17). In those pages, it appears that her speech mostly uses lighter colors for calmer sentences, and darker colors for more heated ones. The particular color doesn't seem to make much difference.
Most of Delirium's speech in this issue is calm; for one example, see page 13 (the one with the butterflies):
However, when Desire provokes Delirium (by calling her "Delight"), the speech bubbles take a darker hue (page 17):
Note that in these panels, the colors blue and green are used for more forceful speech, unlike what the various wikis posited. However, those colors are darker than the ones used before. It might even be possible to interpret the last two bubbles by Delirium in the above picture to contain an increase in both volume (the huge, bold word "GOD") and emotion (the shift from white to dark green from left to right).
An interesting difference between my interpretation and that of the anonymous wiki-users is the panel on the bottom of page 16:
There is some reddish-purplish color in this balloon (especially in the tail); however, that color is of a lighter hue. As per Wikia, this should be read as a statement in anger, because of the red. According to my interpretation, this statement has no anger in it, only shock. (And I think my interpretation is more likely, given Delirium's expression in this panel.)