Every time you breed a Paint (unless one is Homozygous for the Tobiano Gene) you take a risk of producing a breeding stock (solid) The best way to remember is:

Tobi to Tobi (both homo) = 100% homo tobi.
Tobi to Tobi (one homo) = 100% tobi - 50/50 chance of producing a Homozygous
Tobi to Tobi (neither homo) = 75% Tobi (25% chance of Homozygous) 25% Solid
Tobi to Solid (Tobi Homo) = 100% Tobi
Tobi to Solid (not homo) = 50% tobi / 50% solid


What I do is make two boxes for each parent, then place the genetic type in each box
example: Horse 1 Tobi (not Homo) first box:Tobi sec box: BS
Horse 2 Tobi first box:Tobi sec box: BS

then take box one 1st horse to box one 2nd horse= Tobi/Tobi = Tobi (homo)
then take box one 1st horse to box sec 2nd horse = Tobi/BS = Tobi
then take box sec 1st horse to box one 2nd horse= BS/Tobi = Tobi
then take box sec 1st horse to box sec 2nd horse = BS/BS = BS

So here you have the 75% Tobi with 25% chance of homo and 25% chance of BS.....of course this is a simplified version but it is the basics.