The color dipole formulation provides an intuitive picture of hard processes in high energy scattering. Most importantly, this approach allows one to calculate nuclear effects in a parameter-free way. I review the relation between the dipole approach and transverse momentum factorization and present numerical results for open heavy flavor production in proton--proton and proton--nucleus collisions. The cross section for heavy quark production off nuclei is known to reflect gluon shadowing, but is also affected by higher twist effects and by finite coherence length effects.

PACS numbers: 24.85.+p, 13.85.Ni