  We analyzed HST images of 31 nearby (z <~ 0.1) 3CR radio-galaxies. We
compared their UV and optical images to detect evidence of recent star
formation. Six objects were excluded because they are highly nucleated or had
very low UV count rates. After subtracting the emission from their nuclei
and/or jets, 12 of the remaining 25 objects, presenting an UV/optical colors
NUV - r < 5.4, are potential star-forming candidates. Considering the
contamination from other AGN-related processes (UV emission lines, nebular
continuum, and scattered nuclear light), there are 6 remaining star-forming
"blue" galaxies.
  We then divide the radio galaxies, on the basis of the radio morphology,
radio power, and diagnostic optical line ratios, into low and high excitation
galaxies, LEG and HEG. While there is no correlation between the FR type (or
radio power) and color, the FR type is clearly related to the spectroscopic
type. In fact, all HEG (with one possible exception) show morphological
evidence of recent star formation in UV compact knots, extended over 5-20 kpc.
Conversely, there is only 1 "blue" LEG out of 19, including in this class also
FR I galaxies.
  The picture that emerges, considering color, UV, optical, and dust
morphology, is that only in HEG recent star formation is associated with these
relatively powerful AGN, which are most likely triggered by a recent, major,
wet merger. Conversely, in LEG galaxies the fraction of actively star-forming
objects is not enhanced with respect to quiescent galaxies. The AGN activity in
these sources can be probably self-sustained by their hot interstellar medium.
