add abr color dynamics

src/canvas.cpp

@@ -900,6 +900,7 @@ void Canvas::stroke_start(glm::vec3 point, float pressure)
     m_current_stroke = std::make_unique<Stroke>();
     m_current_stroke->m_camera.rot = m_cam_rot;
     m_current_stroke->m_camera.fov = m_cam_fov;
+    m_current_stroke->randomize_prng();
     m_current_stroke->start(m_current_brush);
     m_current_stroke->add_point(point, pressure);