answer to the title: YES, totally, but i believe you need a certain inclination to it to make it work.
i've analyzed my own synesthesia (numbers vs colors vs proportions) and after many years i concluded that "its normal"...its just not very common.
Certain brain areas jump to help other parts. So..lets say you have 20units working on a number related task, and 40 idle that would normally process just colors. "Normal" people would use 20unit to process numbers and just that. some people, force their limits and make part of other brain areas to jump in and help. These extra brain power will have its own specifics, and will sometime bring new ways of analyzing information.
For example, for me number 4 and yellow are almost the same. If i see a deformed rectangle,it will have a number associated to it, but because the information is processed by neurons not usually occupied with visual data, it will also have additional information attached to it..such as..feelings. I can positively say that some shapes make you feel more confortable while other shapes can stress you.
My weakest point is language. I was semi retard in that aspect, but slowly other parts of my brain took over language processing and i compensated...not only that i compensated, but i could master 2-3 multiple meanings within same phrase, rhyme, and stuff like that, just by using other brain power such as color and shape dedicated areas.
However when i am tired, those brain sections can't connect to each other same way, and i return to be a retard in talking , almost like now , when i find it difficult to write this post. I assume its also my main problem why i can't read a lot of text..not sure yet.
anyway. With exercise and will, you could train your brain to join forces of multiple areas and manifest synethesia like symptoms