Some precious indications are coming to us from the work of H. Arp "Redshifts of higth luminousity stars..." appeared in Monthly Notices of the Royal Astronomical Society, Vol 258 p.800 by the ADS service over which we would attempt some comments.
1) the K effect (or Trumpler) gives a positivity to the rad. vel. which could increase with the distance (and with the temperature): at least it's not well showed the contrary, while the our a) , b) , c) points probabilize that possibility;
2) the effect K (or Trumpler) is jointed to the luminousity, which is often jointable to the temperature (which is joinable to the B-V, available with 3 numbers approximations);
3) the k1 and k2 situations are frequent and a deeper research could be interesting (expecially after the HTS and Hypparcos data, again in elaboration).