selected.glsl

// vertex shader
uniform float u_selected;
attribute vec4 a_position;
attribute vec4 a_color;
varying lowp vec4 v_color;
void main() {
  if (u_selected > 0.0) {
    v_color = vec4(0.5, 1.0, 1.0, 1.0);
  } else {
    v_color = a_color;
  } 
  gl_Position = vec4(a_position.xy, 0, 1.0);
}

// fragment shader
varying lowp vec4 v_color;
void main() {
  gl_FragColor = v_color;
}