Re: Color of yellow Be treated sapphires compared to untreat
It's impossible to tell. You have all strengths of colour in both BE and also natural yellows. I've seen some paler BE stones that had I not known, I would have sworn were natural. Then I've seem some highly saturated vivid ones that I would have said were BE and they were natural. It's the one colour sapphire that I'd never lay money on whether it'd been treated to alter colour!
Re: Color of yellow Be treated sapphires compared to untreat
Diffusion can be done to sapphires to show all the various colours from yellow all the way to red and blue. I've also seen the super saturated eye popping ones and the grayish looking ones. Having vivid colouring is no longer the definitive way of spotting a diffused sapphire.