I dislike reducing things so others that would try and pull me up I am aware of many issues with what follows- do read my other posts in this thread though.
In a paragraph
Shape, size and colour- probably not worth the effort of even learning it. Far better to find a trustworthy dealer (others reading please spare us the "obvious" remark).
Combinations of different drugs- absolutely. Alas the modern world has seen monetary profit be the choice motivator and some of the modern combinations are not (or more worryingly potentially) that brilliant for you versus some of the safer or in many cases unmixed varieties that have been studied more extensively.
New recipes (thinking actual new things that are not traditional MDMA rather an isomer or tweak to a functional group*)- again absolutely. Same logic as the straight up mixing applies though.
The OP though does not appear to be too much of a scientist (who does not love a bit of Hubble imagery?) so that surely has to inform my replies here.
*again I direct you to Tihkal and Pihkal- two books, hundreds of resulting chemicals with radically different required dosages to do things (to say nothing of mixing things) and effects but still effectively two classes of chemical (one for each book).
More waffle
I am certainly not denying that new pills are being made and methods being dreamed up for all sorts of reasons (suppliers of certain chemicals changing up or things getting restricted- see some of the elaborate workarounds for those producing meth amphetamine, increasing strength, making it easier to do, making it less troublesome for those doing it, making it cheaper, upping yield, changing levels of byproducts/reducing issues with purification and so on and so on). Indeed in many ways I admire some of the people in this world- in many ways they are some of the best industrial and research chemists out there.
What I was saying though is any fool can make any pill containing whatever they like into any shape with any colour and any design they like with no trouble at all and they do it all the time.
Combinations of chemicals
No argument here either- it is mixing things together that got us where we are today and there is always the potential for something better out there (at least until we crack biology and even then there are other considerations) so it will continue. I do urge caution though as especially at the levels we are now playing at things can change extremely easily from simple changes- it is one of the things that makes chemistry, especially things like pharmacology, so very interesting to be involved in.
Edit: Re: "Does what it says on the tin"- I always thought it was a fairly common phrase but that might be the fault of Ronseal and equally might be one of the more UK centric phrases.