I've tried 2 sets of no name LEDs, but each time I notice a partial yellow cast/tint on the wall/vehicle in front of me.

And after looking at the bulbs up close, my hypothesis is that the cheaper bulbs have diodes that are, well, bigger than the area of the filament (halogen) and the yellow tint is actually reflected off the diode base.

Am I correct to say so? If not, is it just an issue of headlight leveling?

 

Are you talking about the color of the light in general, or the pattern of the light?

The color of the light is inherent in the LEDs. It shouldn't change much if any with angle. The pattern using any LED headlight bulb is going to be bad because the light pattern produced by the bulb is wildly different from a real halogen bulb and not in the designed focus position for the headlight reflector. That's why LED bulb replacements, at least those sold in the USA, are marked for off-road use only and not legal for street use. (These laws are not always enforced very well, rather to my dismay at times.)

You would not see much if any coloration from reflections from the LEDs. Their yellow color is, I suspect, due to the phosphor on the white LED chips. White LEDs are generally blue LEDs with a phosphor that absorbs some of the blue light and emits yellow-green light that, when combined with the remaining blue light, gives something sort of like white light. (LEDs are inherently monochromatic light sources so cannot produce white light directly.)