Jim;
I totally agree with using Brennan’s ballast. Now, I am only using Lionel Fastrack, so it is not as critical for me, but I definitely like the look of the added stone. And as you mentioned, mixing the various ballasts can give you different shades. The ballast is pretty small...
I have been mixing the yard ballast with the standard gray ballast... I am currently doing my engine yard, so I have been mixing 2 cups of yard to 1 of standard for a darker appearance...
I used a lighter mix (2 standard to 1 yard) for my main lines...