That pair of
black shoes are is
bigger than this blue one.
I think it would be more natural to say "bigger than the blue one" (unless there is an assortment of blue shoes, or shoes of other colour, for that matter. But it´s a matter of choice of words, there´s not grammatically wrong with "this blue one" if you are near it.
Notice that the "pair of black shoes" is "one pair" so the verb to go with is to be, "is" in this case.
Also notice that you used ''that pair of black shoes", if it´s "that" then it would be along with "is".
These blue tennis shoes are cleaner than that green one.
To me the sentence is a bit imperfect as it is, with "these" you are comparing a pair of blue tennis shoes, or several blue tennis shoes (it´s not specified in the sentence if it´s a pair, but we can assume that, though.).
Again, "these" goes with "are", and since you were talking about "shoes" in the beggining you might have put "green ones" at the end of the sentence.
The logic/reasoning behind it is:
Step #1 - "blue tennis shoes" (plural, hence the "these" there.) Then, it would be compared with the "green ones".
Step #2 - Forcibly, if in the sentence you have "green ones". Then the demonstrative pronoun would be "those" (plural of "that"), of course, if we maintain the contrast "things near" versus "not near us", wich seems like being a pattern kept from the first sentence on.
Thus, the final sentence would be:These blue tennis shoes are cleaner than those green ones.
I hope I have clarified your doubt.https://learnenglish.britishcouncil.org ... -and-thosehttp://forum.wordreference.com/showthread.php?t=42009