We propose an effective one-component model that accurately reproduces the colloid-colloid radial distribution function g(cc)(r) of a colloid-polymer mixture. The particles of this effective model interact through an effective potential u(eff)(r), obtained by inversion of the Ornstein-Zernike equation and a closure suited for fluids with repulsive cores. The consistency of this approach was tested by simulation of the effective one-component fluid and comparison to the original radial distribution function. The effective potential can be separated into a repulsive part (corresponding to the "bare" pair potential between colloids), and a depletion potential, v(r). The strength and range of v(r) are well represented by simple functions of the total volume fraction. (C) 2003 American Institute of Physics.