You can buy proper tyre wall white paint in a tin.
Frost Auto Restoration Techniques - Search Results for tyre wall
Haven't tried it myself so not sure what it's like.
I guess half the problem could be if these tyres are already used and you have used some tyre wall blacking stuff. Most of these contain silicone and will soak into the tyre wall itself. Not a lot sticks to silicone.
Craig.