If I were to write buy 2 blue and/or red towels, would I be saying:
Buy 2 red towels, 2 blue towels, or 1 red and 1 blue?
Or
Buy 2 red towels, 2 blue towels, or 2 blue and 2 red towels?
If I were to write buy 2 blue and/or red towels, would I be saying:
Buy 2 red towels, 2 blue towels, or 1 red and 1 blue?
Or
Buy 2 red towels, 2 blue towels, or 2 blue and 2 red towels?
In most instances, you would be communicating that any combination of two blue and red towels fits the bill. Unlike a mathematical equation, english speech does not include parenthesis to disambiguate the permutations.
If clarity was required, one could be more exact:
The and/or implies selection, however, and as such 4 towels would be the less expected choices. More likely, one wishing to communicate this option would say:
The inherent choice of and/or, however, would suggest that once the permutation is known, that it not be used. For example "He bought 2 red and/or blue towels" is rather silly. One would normally write what happened. Alternatively, "Customers could choose between 2 towels, red and/or blue."
In all cases, however, the ambiguity could be easily clarified by a better construction.
It is not clear from the way you have written this sentence what you intend to say.
'and/or' is a particularly vague modifier - as a conjunction, it can mean and OR or, or both, and there is no clarifcation as to which is being used. The '/' symbol is being used as an additional 'or' statement, making it impossible to tell which conjunction you are using, or if you intend to somehow combine the two.
Any of the interpreations you offer are valid interpretations of that sentence.
To clarify that you only desire two towels, but that they can be of either color, a better construction would be:
Buy two towels. They can both be either red or blue.
This clarifies the number of towels you want, and then clarifies that both towels can optionally be red or blue, and that neither color of towel is dependent on the other towel's color. It is true that this requires more words to say, but if you value clarity over brevity, it is far superior.
Let's look at the two options:
If you meant 2 total, expanding the and/or you would be saying:
(A)
Expanding the and/or, if you meant 2 of each, you would be saying:
(B)
As this second interpretation (B) seems like a very strange request (you are asking me to buy 4 or 2 towels), the first interpretation (A) must be considered the only valid one.
So I might buy one blue towel and one which is red and blue.