I have a model file that looks great with 5 colors, I understand that filament on my external spool is not automatically loaded (no drive) but if I select the color least used, how do I feed from external spool?
Will it stop printing and prompt me to load and then unload that color before resuming from AMS and do so again when required. If not, what do I do?
Thanks
There is currently no way (as far as I know) to utilise the external spool while also using the AMS opportunity.
It is one or the other.
If your model uses 5 colours and you have access to a single 4 spool AMS, it is still possible, one old way, often the best and one new way, possible, if the colours chosen work out.
Old way, my preferred
Provided you model doesn’t use all 5 colours in the same layer, you can simply swap out one spool at the correct time to use the fifth colour.
I first played with it on this print profile for a model designed by a different designer.
https://makerworld.com/en/models/103244-articulated-teddy-bear-print-in-place#profileId-175273
The bear has five colours, brown, beige, black, white and red. (The text below formatted poorly due to this editor, it is dumb).
I painted this so the white eyes were painted red, this is important.
I added a PAUSE command at a layer above the bow tie and before the white pupils are printed.
When the print pauses, remove the red spool and replace it for a white spool, resume and you have five colours. You can extend this to any number of colours provided, you never have more colours in any one layer than your AMS units can deliver and you can plan the PAUSE commands and the swaps, so you do not do them out of order.
I also used the logic on many of my own models, this is one. It uses 7 colours and can be printed using a single AMS.
https://makerworld.com/en/models/501459-proud-willy-articulated-fidget-toy-keychain#profileId-416515
Combine colours
The latest versions of Bambu Studio allow you to mix two colours together from the ones in your AMS to visually appear as a single colour.
If you remember back to your childhood school art classes, you will remember mixing colours. Your 2D printer uses a version of CYMK to print full colours.
You can do the same on your 3D printer.
It is achieved by using thin layers of one colour, then a different one, then repeating. It is best used for edges and becomes less visibly mixed on sharper angles like curved surfaces.
You simply need a recent build of Bambu Studio. Look under the filament chooser in the prepare tab, to see a new option. Add a new mixed filament and choose two different colours you have already added to your palette. That new colour(s) becomes as accessible to paint or colour parts as any standard single colour.
Three caveats:
I’m using the latest studio - so that “mix colour box” I thought was to be used with one of the multi colour (I noticed) filaments - my bad. I can’t see me mixing colors and my childhood was back when they used an abacus to teach math.
That external spool seems a bit useless then, other companies provide drives to their spools that are external only so maybe its mod that can be created.
I’m new to this game and stumbling along with my learning, I think I’m going to set up something small using the external holder as an early color just be perverse and see what happens 
It serves a function, several in fact.
The form and function depends on the printer. This use is also very new. Many printers like the U1 from Snapmaker uses motors to load filament from external spools. An excellent printer which I believe is a massive leap forwards. Yet, it can’t use an AMS or equivalent, so it gains a drive assist, and loses and AMS.
Bambu Labs recently introduced a TPU Feed Assist module that aids loading filament through the external inlet. It doesn’t solve your problem and still requires a little manual intervention, but makes the whole thing easier. I haven’t installed mine yet, but the consensus is positive.
Bambu Studio recently gained the ability to treat the external inlet like a poor man’s AMS, it lets you pull up a chair next to the printer and be responsible for swapping external spools out to gain the same sort of multi material benefits that an AMS allows, but with significantly increased manual involvement.
I mention this as it makes it more likely a future release may allow the external inlet to be part of an AMS ready solution.
Hi, Thanks for your reply. Yes, it seems that for every step forward there are some losses.  Your penultimate sentence addresses my thought that there must be a way to manually intercede when the fifth color has a limited number print lines.
For clarity, while I investigate the “TPU Feed Assist module” I had bought some TPU to print some model tires, but the model wouldn’t address my P2S even though I was prepared to load it manually. If I designate the external spool for few lines with the remaining colors in my AMS would it look for the manual feed and halt? Sorry if I asked that before.
I can now answer my own question = NO
Notes：
1.When the left hotend of the H2D is connected to the TPU Feed Assist Module, multi-color or multi-material printing is not supported (the left and right hotends cannot be used simultaneously). This is because the lifting movement of the left hotend will affect the feeding stability of the assist module, which in turn leads to extruder clogging.
2.The TPU Feed Assist Module must be used with an external spool holder, and does not support the automatic loading and unloading function of AMS. It only supports manual feeding through the TPU-dedicated filament outlet of AMS HT.
It’s a little confusing that most of the comments concern dual head machines and AMS HT, but I guess it also applies to P2S and AMS Pro 2
As you said - maybe in a next step.