Add missing hints for color conversion methods.
Add missing hints for color conversion methods.

This also changes the obsolete "2307" code to simply "307", the type
code for "double *".

msmolens/VTK,SimVascular/VTK,sankhesh/VTK,sankhesh/VTK,msmolens/VTK,mspark93/VTK,candy7393/VTK,candy7393/VTK,msmolens/VTK,keithroe/vtkoptix,SimVascular/VTK,keithroe/vtkoptix,sankhesh/VTK,sumedhasingla/VTK,sankhesh/VTK,jmerkow/VTK,sumedhasingla/VTK,keithroe/vtkoptix,jmerkow/VTK,msmolens/VTK,mspark93/VTK,SimVascular/VTK,SimVascular/VTK,msmolens/VTK,keithroe/vtkoptix,keithroe/vtkoptix,SimVascular/VTK,candy7393/VTK,sankhesh/VTK,gram526/VTK,mspark93/VTK,jmerkow/VTK,gram526/VTK,sumedhasingla/VTK,sankhesh/VTK,sumedhasingla/VTK,candy7393/VTK,gram526/VTK,demarle/VTK,sumedhasingla/VTK,candy7393/VTK,demarle/VTK,candy7393/VTK,gram526/VTK,SimVascular/VTK,mspark93/VTK,gram526/VTK,mspark93/VTK,demarle/VTK,mspark93/VTK,sumedhasingla/VTK,sumedhasingla/VTK,keithroe/vtkoptix,demarle/VTK,jmerkow/VTK,jmerkow/VTK,mspark93/VTK,msmolens/VTK,gram526/VTK,mspark93/VTK,SimVascular/VTK,keithroe/vtkoptix,jmerkow/VTK,jmerkow/VTK,candy7393/VTK,candy7393/VTK,msmolens/VTK,SimVascular/VTK,gram526/VTK,demarle/VTK,sumedhasingla/VTK,demarle/VTK,msmolens/VTK,demarle/VTK,sankhesh/VTK,keithroe/vtkoptix,gram526/VTK,jmerkow/VTK,sankhesh/VTK,demarle/VTK