Dh needs the computer so no time to write a proper response tonight but I think text fading is the way to go here.
You will need to use ABA approaches as you say: however, I believe there is potentially some merit to teaching the colour coding here.
There is a resource here that shows really what needed to happen between initiating for single objects and the multiword utterances you have now: www.tulareselpa.org/Autism/Downloads.shtm
e.g. three meaning relationships e.g. Jamie eats fruit loops where one word/phrase corresponds to one bit of meaning.
What your ds appears to be doing is remembering chunks of language associated with a specific context and assembling them in this way - it's just that the context/assembling is somewhat idiosyncratic to him. The best example of this is the "why"//"because the do you want the dinner?" example. So "because" is associated with "why" but getting what he wants is associated with "do you want the" and then he is saying "the dinner" as he could probably (I'm guessing here, maybe not) also change this element to be
"because the do you want the breakfast".
So it is two to three meanings he is using here with seven words, either:
[because the] [do you want the] [dinner]
or
[because the] [do you want the dinner]
The longer elements don't quite fit together in the way they should for this reason.
Nothing wrong with using a lot of words corresponding to each meaning, it's how we build up complex meaning... except of course he is breaking the rules for how we do this so although you understand his meaning the grammar is all over the place and, where it is truly idiosyncratic, even you can't work it out.
However, can I say that the first example, is a really positive sign that he is working hard at the rules.. I would expect he has had a few "goes" at this. The other great positive is that he is really aware that he needs to initiate with you so is using markers for this..
He may need some help with getting it straight though (as I guess you've figured).
Can he sight read at all? I know you said it to highlight the issue with the intervention but might be a very valuable tool here. If he could sight read, I would be inclined to
deal with these in the moment using pen and paper e.g.
I think in the first example, he is asking can he go in the kitchen - not why at all..
so
if he says:
'why do you want the can I have the mummy go in the kitchen please?"
and he could read,
I would write
"Can I go in the kitchen please?" and get him to read it and then say "Why?" and then
when he responds with
"because the do you want the dinner"
write
"because I want dinner" Then, having done this, I would start to tackle these questions using communication temptations, changing the place/what he wants e.g.
"Can I go in the bathroom?" "Why?" "because I want the [insert reinforcer]"
Then you fade the text so..
Can I go in the kitchen please
Can I go in the kitchen
Can I go in
Can I go
Can I
Can...
eventually fading out all text prompts
I can blend this with the colourful semantics too if you want.. I would be thinking of using the sentence stems to teach different places with the colour.. e.g. kitchen/bathroom/bedroom etc.
I just need to think some more about it..
Does any of this make sense?