It is very easy to mistakenly separate parameter names from their type description by ': ' instead of the correct ' : '. There are at least 260 instances in Scikit-learn, for instance, and Joblib appears to use : without a preceding space as a standard. This variation is unsurprising when See Also, for instance, does not require a space before its colons.

Would we expect great ramifications were we to change it to allow a single colon followed by whitespace as delimiter?