------------------------------------------ -- -- -- -- --
      *U–u & *B–b & *V–v & *U–B & *B–V & *U–V\              
           *u–b & 202 & 102 & & 102 & &\                    
              *uvw1–u & 222 & & & & &\                      
        *b–v & & 211 / 3 & 111 / 2 & & 1 &\                 
              *uvw1–b & & & & 102 & &\                      
             *u–v & & & & & & 101 / 1\                      
            *uvw1–v & & & & & & 102 / 1\                    
                    ************                            
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  : Summary of the colour transformations established in this paper. Capital letters refer to Johnson $U$, $B$ and $V$ filters. A one, two or three digit code [$i_1,...,i_n$]{} characterizes the transformation: $n$ is the number of temperature domains that have to be considered; $i_k$ is the order of the transformation in the $k^{\rm th}$ domain (0 means no transformation is possible), e.g. 102 indicates that one has to divide the temperature domain in 3 distinct parts in which respectively linear, no and second order transformations are possible. The numbering of the domains is going from the hottest to the coolest stars.

We restricted ourselves to a limited set of physically meaningful transformations, i.e. between equivalent 