What's up with the colors of Delirium's speech bubbles?

Question

In the prologue to Season of Mists (The Sandman #21), the Endless are gathered for a family meeting. Each of them talks with a different typeface, to help differentiate their manners of speech and personality.

I'm wondering why Delirium speaks with colored speech bubbles. I understand that the shifting font size shows her to be slightly tipsy and not quite coherent, but I wonder what quality of speech might be indicated by the changing colors of the bubbles. Is it just more of the same, or do the colors indicate something else about Delirium's speech? (Whimsy, perhaps? My brother noticed that the colors of the speech bubbles in one panel matched the colors of the butterflies that Delirium created.)

Take this example from page 8, with three or four different colors in the bubbles (left), and the panel with the butterflies from page 13 (right):

Answer 1

It was a decision by the letterer, Todd Klein. As he explains in The Sandman Companion, it was supposed to reflect her fluent, shifting nature:

Delirium was a different challenge. "Her lettering constantly changes in size, shape, and slant, wobbling in out, to indicate that she's always on the verge of madness," Klein says. "Her balloons also contain a variety of rainbow colors, which was my idea but executed by the colorist Danny Vozzo."
_{The Sandman Companion, "Secret Origins - Origins of Lettering Styles", page 245.}

I took the changing typeface to indicate Delirium's changing voice volume, and maybe pitch, while the colour could indicate her overall (inner) mood.

Klein most probably took the "on the verge" part from Gaiman:

NG: [Delirium] is a character I wanted in a state of flux - she's been one thing, she's become something else, and eventually she'll change into something else again.

HB: Is this state of flux unique to Delirium?

NG: Yes. It has to do with her being the youngest; she's practically a cosmic afterthought.

If you flip through Brief Lives, you'll see that Delirium's look is constantly changing, pretty much whenever the mood strikes her, so it's easy for Delirium to look like several different people.
_{Ibid, page 241.}

Answer 2

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.

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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.)