The way that genetics work with blue, black, and splash chickens, you are able to calculate the percentage of each color that you will get from each breeding by using a punnet square (or at least in theory, such as out of 100 chicks, with small hatches the percentages can be off, but in general out of a lot of hatchings the percentages should be accurate). It's not a 'most likely' thing - when breeding a blue copper rooster to a black copper hen, you will only get blue copper and black copper chicks, no splash. If you're confused I would be happy to explain how to do the punnett square and how it works

You can do the same thing with other simple genes like the gene that causes a chicken to be a naked neck.
Edit: Actually I'm going to go ahead and explain how the color works for anyone that comes through here in the future. Blue, black, and splash genes can be written out like this.
Blue, when talking genetics, is usually written out as Bb, and black is bb, and splash is BB. These are how we write out the alleles. Using this, we can do a punnett square to see how breedings would work and what color we would get from each breeding. So if you were to breed a blue (Bb) to a black (bb) the punnett square would look like this:
Looking at this square, we can see that we will expect half of the chicks (50%) to hatch blue (Bb) and half to hatch black (bb).