[9.5] Can I set different colours, fonts etc in a single field via lingo?

Yes. Contrary to the evidence of the Lingo manuals, most of the cast text properties may be specified for chunks as well as for entire fields. An example of each follows:

set the textStyle of word 1 of cast 20 to "bold"
set the textSize of char 10 of field "bingoBangoBongo" = 18
set the textFont of char 1 to 5 of cast "hello" = "Helvetica"
set the foreColor of item 1 to 6 of field 12 to 128

The textHeight and textAlign properties can't be set for chunks. A command such as:

set the textHeight of line 17 of cast 90 to 28

will be accepted, but the textHeight will be applied to the whole field regardless.

Attempting to set the textAlign of a chunk results in a script error.

However, these methods do not seem to be 100% reliable, so use them at your own risk.

[Caveat: see section 1.8]