We thrive on the unusual, because it is the unusual which advances our understanding of how various kinds of objects 'work'. Depending on what we are trying to investigate, we construct various 'filters' to weed out objects which do not have the desired characteristics. For example, if we want to search for very distant quasars to study how different they might look from nearby ones, we take advantage of the cosmological redshift. The very bright optical emission in the 'blue' part of the spectrum used to be the way that quasars were discovered as unusually 'blue' stars. But at redshifts from 3 to 5, the light from the blue part of the spectrum is shifted into the infrared. So, to find very distant quasars, astronomers look for star-like objects in the infrared that are 'very blue', meaning that they emit more light in the short-wavelength infrared bands than is expected from ordinary stars.
If you have a new kind of telescope that is sensitive to X-ray, far-infrared or radio radiation, the bright objects you discover at these wavelengths may be unusual. A comparison of their positions with the cataloged positions of known objects at other wavelengths, particularly optical, will tell you if you have detected a new kind of object. Astronomers spend a lot of time creating new, special purpose catalogs to highlight exotic properties of stars and galaxies.