There are many models where you cannot avoid using support materials. However, these supports can leave marks on visible surfaces which are not very nice. Bambu Studio gives you the possibility to print the contact surfaces with a different material. For this feature you need AMS which is a very useful feature besides the colour printing option. You can use special support material or pairs of materials that do not adhere to each other. For example PLA and PETG.

Enable the usage of support.
Select Support/raft base material. PLA
Select Support/raft interface material. This should now be PETG
The Top and Bottom Z distance can be zero. This is possible because the two different materials do not stick together. But feel free to experiment with the spacing or the pattern of the contacting interface to get a better result.

Now comes the point. When changing the colour, it is not enough to clear the colour completely but there must be no remaining different material in the Hotend and the nozzle. In this case, you will push the contaminated material into the object, which will break easily at this line.

For the Flushnig volmes, the volume of the flushed material in mm3 should be given. In the example I want to wash the blue PETG material well with the green PLA. The default value is 280 which is usually enough but in this case it is certainly not enough. I increased the flush volume every 100 mm3 and performed a breakage test. Usually they recommend a max of 800 but with this test you can bring it down a bit. This can save time and material.

280 and 380 broke easily. At 480 it was noticeable that it resisted more. 580-680 gave a good result although I managed to break it at the same layer but I had to use considerable force
I had to take the flushing volume up almost to the maximum value to get the right result. These values can vary considerably between manufacturers and combinations. If you are using specifically support filament then this test can be avoided. However, these materials can cost several times more than normal filaments.
As a lesson learned and as a word of advice, do this test to be sure of the strength of the finished part. This will avoid unwanted breakages, wasted material and many wasted labour hours.
Until I forget. Don't throw away the break-off pieces, they are exactly 0.1 inch (2.54mm) thick. I'm sure they'll make a good filler somewhere. 😊

model origin: https://www.printables.com/model/380716-oh-deer