Sorry if this may sound noobish. My K3 is my first and only reader and after reading a number of different books I noticed that each book has a different level of font clarity. I downloaded the Sherlock Homes collection from mobileread and compared it to the same full collection I bought from Amazon. The one from mobileread seems to have a darker font. Is this a common occurence or its just my eyes playing a trick?

My copy of the Homeland(Drizzt series) has a very very dark font, it is as though it is in bold.
So the question is, is there any method to change the native font type of a particular epub/mobi file before uploading it into my kindle via calibre?
Thank you so much.