1: Is the technique of setting object attributes via messages documented anywhere?

(x2.html has most things, but I don't see this.)

Right click on an IEM gui (tgl for instance) and choose help. Then open the “edit” subpatch.

2: Is there a list of all the standard objects, and the names of all
attributes (methods) which are settable via messages?
(A language specification or reference should have this)

See above.

3: If I send the message [color $1( to an object, say a tgl,
it seems to follow an index into a table (modulo 30)
which corresponds to the little table that comes up in
the object properties dialog box:

<object color table.jpg>

So my last question is, can I rely on that table staying
the same across all versions of PD? Will index 13 always
be Red?

Yes.

4: Can I change that table?

No, but as mentioned in a previous replay, you can compose your own colors as well and set them via messages.

5: I would prefer to set an object's color via an RGB value
Can I do that?