SpineyPete

float PhongBase(vec3 viewdir, vec3 lightdir, vec3 normal) {
	return max(-dot(viewdir, reflect(lightdir, normal)), 0.0);
}

// Analytic specular without ambient specular might look better like this.
float HalfPhongBase(vec3 viewdir, vec3 lightdir, vec3 normal) {
	return -dot(viewdir, reflect(lightdir, normal)) / 2 + 0.5;
}

// Something to approximate the longer tail

SpineyPete

#version 330

// Colorspace conversions, I haven't checked the validity of this stuff.
// Some of them cause discolorations when transformed to and back so I'm
// probably doing wrong things that I don't understand -- Caveat emptor.

// CIELab XYZ
// ----------
// Matrices borrowed from Fundamentals Of Computer Graphics (3rd edition).