Cosplay Boot advice

So I did show these off before but I was looking for any kind of putty (or anything similar) that I can use to fill in any of the gaps Between the seams on the shoe. The filler should be -Flexible -can be colored over with shoe polish and/or paint -works well with vynil. Any suggestions would do. If you need to know how I glued the vynil on, I made a template cut out the vynil and use contact cement for gluing.

I have slight gaps in the front and want to find something that can cover them and the seams on the sides when I am done. anything that anyone can recommend?