That Wammy Boy stare.
Or - eye colors, symbolism, and my head canon about L, Near and Mello's "weird dead eyes".
In Volume 13 Takeshi Obata reveals that because Ohba requested Near and Mello each have something reminiscent of L in their character designs he decided to express this by giving them the same eyes as L. As a result in the manga all three have black seemingly iris-less eyes.
So are we meant to understand that they all actually had pitch black pools where most humans and indeed everyone else in the manga had normal human eyes including the luxury of colored irises? On the other hand, in the anime L retains his familiar black eyes, however Near's are grey and Mello's are blue.
So why the inconsistency? In my opinion....BOTH are true.
It's not impossible to have eyes that are so dark brown they appear practically black, and the line between iris and pupils becomes hard to distinguish. But Near and Mello both have very fair skin and hair, it makes sense for them to also have light eyes.
My interpretation is that Obata's intent here is meant to be more symbolic than literal. Their black eyes may indeed actually be brown, grey, and blue respectively. But the similarity Obata tries to convey is not in the surface of their physical appearance, it's their essence that shines through. It's what I will call the "Wammy Boy stare" (admittedly something of a misnomer because it's really only a quality shared by L and his successors, but bear with me I wanted to use a catchier term).
The stare is the feeling those eyes project, the unnerving sense that they observe and analyze everything around them. That they can see into your soul, through and past you, and against your will can unearth your sins. That they know what makes you tick and just what buttons to push. That they know something you don't. It's in equal parts mysterious and alluring and intimidating as fuck. It's psychic damage, a feeling of exposure, a gaze that can make you squirm and stammer and reveal your secrets. Eyes that see everything but reveal nothing about the mind of their bearer.
Since I like to try to ground my theories in at least a crumb of source material, this ties in also to Near's comments in the C-Kira one shot where he said the reason L singled out himself and Mello and chose them as his potential successors was because of how they observe, and "the nasty look in our eyes".
In conclusion: Near has grey eyes, and Mello's are blue. But they are both distinctly L's.
