Just to confirm I'm adjusting the ambient light correctly in the fragment shader, I've added the below lines
float specular = pow(clamp(dot(reflect(-lVec, bump), vVec), 0.0, 1.0), 0.85);
vec4 vSpecular = vec4(specularColors[0],0) * specular;
vAmbient.x += 0.3; // ADDED
vAmbient.y += 0.3; // ADDED
vAmbient.z += 0.3; // ADDED
gl_FragColor = (vAmbient*base + vDiffuse*base + vSpecular) * att*2.0;
}