FYI
Given @cap's clever visualization solution, following recursive formulas:
- number $g(n)$ of grey triangles
$g(n)=n>0$$g(n)=n==1$ $?$ $1:g(n-1)+(2*n-1)*(n\%2)$
- total number $t(n)$ of triangles
$t(n)=n>0$$t(n)=n==1$ $?$ $1:t(n-1)+(2*n-1)$
confirm $45\%$ for $n=10$
I found no OEIS® entry for grey, white or total series.
The highest amount $n$ of rows with an integer percentage $p$ of grey ones seems:
$n=50$ with $p=49\%$
Also, if we write $w(n)$ for number of white triangles, then following non-recursive equations hold
$t(n) = g(n) + w(n) = n^2$
and
$w(n) - g(n) = (-1)^n * n$
And, if we write $x(n)$ and $y(n)$ for the alternating smallest and biggest one of $w(n)$ and $g(n)$ then
$x(n) = n * (n - 1) / 2$
and
$y(n) = n * (n + 1) / 2$