It has previously been found that radio galaxies are sometimes rather
blue (Smith & Heckman 1989) and that the same appears to be still more
the case for quasar galaxies (Véron-Cetty & Woltjer 1990, 1997).
This trend is confirmed by PKS 1814-637 and PKS 1934-638, the latter of which
is known to be a very compact double. Long ago Shklovsky (1965) predicted, soon
after its discovery, that PKS 1934-638 should diminish in flux quite rapidly, if
an expanding source. It was found however to be quite constant (being used now
as an Australia Telescope standard: perhaps imprudently?) and therefore it
should be located in a high pressure medium that confines it. Nevertheless
such a compact object should be relatively young.
Blandford (1990) has proposed that strong radio sources are associated with rapidly rotating black holes and that accretion at close to the Eddington rate is required to reach the necessary angular momentum. Therefore as we discussed before (Véron-Cetty & Woltjer 1997) we should expect that if, as in the Seyferts, gas is supplied rather slowly not much radio emission will result. However in major mergers gas is supplied to the nucleus of the galaxy in adequate quantities to produce a strong radio source and also a high rate of star formation. The black hole would be spun up on an Eddington time scale of a few 108 years and at the same time star formation would produce a generation of luminous blue stars. The shake up from the merger would lead to a global r1/4 luminosity profile resembling that found in typical ellipticals (Barnes 1988), but during a time of the order of 108 years the elliptical would be rather bluish. In such a picture, strong radio emission would not so much be a property of ellipticals, but rather would be a consequence of the mechanism that forms (some of ?) them.
The case of PKS 1353-341 is perhaps not very different. Here there is evidence for a possible merger taking place at the moment. However the cD galaxy is so luminous that the addition of some blue stars would not very much affect the colour of the main body of the galaxy.