WordWeb Online

1. [Brit, Cdn] In violation of good taste even verging on the indecent
   "an off-colour joke";
   - indelicate, off-color [US]
    
2. Humorously vulgar
   "off-colour jokes";
   - bawdy, off-color [US], ribald
    
3. [Brit, informal] Somewhat ill, feeling or being in bad health
   "my poor off-colour grandmother";
   - ailing, indisposed, peaked, poorly, sickly, unwell, under the weather [informal], seedy [archaic], out of sorts [informal], grotty [Brit, informal], crook [Austral, NZ, informal]

See also: dirty, ill, sick, tasteless

Encyclopedia: Off-colour