A material is transparent if it transmits photons which continue in their original direction, or are all deflected by the same change in direction. Such transmitted radiation retains any image which it had when it entered the material. Transparent materials contain very little crystalline material and their atoms and molecules are arranged in an irregular pattern making them glassy or amorphous. This induces negligible scattering because the net effect of any scattering that is induced is zero. Materials may be transparent to some wavelengths of light but not others.
Visible light has a limited range of wavelengths.
Even so, different wavelengths are seen as different colours. Some materials may be transparent to some colours but opaque to others which explains, for example, tinted spectacles.