In images like these, I notice how in the glow area, well look at the block in the first screenshot - it looks green! - and in the second screenshot Mario looks like he has a sunburn!
What is the cause of this?!? If stuff glowed like that in real life I'd probably put the source in a biohazard bin!
It's the combination of the yellow filter onto the brownish background. That's just what this two colors look like together. I really don't understand what's confusing you here.
Mario's face is peach, and the glow is yellow.
Ideal combination = a lightish yellow peach
The game combination - Yellow and Magenta?
Zoom in closer if you don't notice.
Graphics processing doesn't work like real life. Just because Mario's SKIN TONE and the yellow glow mix together to form a lighter flesh tone colour in real life doesn't mean the graphics will process that. It's actually simple knowledge to comprehend.
Yeah, none of the default graphics use translucency (i.e. transparency with color). Redigit probably didn't expect this kind of effect to become as popular as it has. It's really not that big a deal.
It has to do with the way masks are interpreted in SMBX - I haven't studied this, but I'm guessing it's because the mask controls how much light is let in based on what color (or shade of gray) it is. This would, ostensibly, leave it up to RGB-style coloring/lighting with pigments and lights and stuff you learn about in a physics class.
Yes, these are your glowing Baby Yoshi screenie tests - please be on topic.
You can just say "Blame Redigit", but here's a longer reason:
Since Redigit was drunk, the interpretation of the transparency of masks through coding went horribly wrong, which can change palettes and make some sprites look 8bit, which means that the coding is a bit weird for the masks.