X1 -2.0
Y1 1.0
X2 1.0
Y2 -1.0
R/G/B = 255/2.55 * iter/0

X1 -2.0
Y1 1.0
X2 1.0
Y2 -1.0
R/G/B = 2.55 * iter/2.55 * iter/2.55 * iter

X1 -0.37465401
Y1 0.659227668
X2 -0.37332411
Y2 0.66020767
R/G/B = 2.55 * iter/2.55 * iter/2.55 * iter

Random images

C source code:
mandelbrot.c
timer.h