1. A control apparatus for controlling a printing device configured to print a color source image together with a white base by using color materials of a plurality of colors including cyan, magenta and yellow for the color source image and a white color material for the white base, the control apparatus comprising: a raster-image processor that creates multi-valued pixels forming a color source image and multi-valued pixels forming a white base; and a hardware processor that makes a judgement whether each of the multi-valued pixels forming the color source image is colored in one of specific colors, controls an amount of the color materials to be used in printing the color source image together with the white base, by reducing pixel values of the multi-valued pixels forming the color source image and pixel values of the multi-valued pixels forming the white base so that a total sum of the pixel values corresponding to colors of the color materials of the color source image and the pixel value corresponding to white of the white base at a same printing position becomes a predetermined value or less, by using screening, converts each of the multi-valued pixels forming the color source image and each of the multi-valued pixels forming the white base given after controlling the amount of the color materials, into matrixes of two-valued pixels corresponding to the colors of the color materials of the color source image and a matrix of two-valued white pixels corresponding to white of the white base, to create sets of two-valued pixels corresponding to the colors of the color materials, forming the color source image, and a set of two-valued white pixels forming the white base, and rearranges the two-valued white pixels, including using the matrixes of two-valued pixels corresponding to the colors of the color materials of the color source image, obtained by converting each of the multi-valued pixels judged as being colored in one of the specific colors, to determine first pixel positions at each of which at least one of the two-valued pixels corresponding to primary colors of cyan, magenta and yellow is colored and second pixel positions at each of which none of two-valued pixels corresponding to the primary colors is colored, using the matrix of two-valued white pixels, obtained by converting the multi-valued pixel forming the white base corresponding to the each of the multi-valued pixels judged as being colored in one of the specific colors, to rearrange at least one of colored two-valued white pixels at either of the first pixel positions or the second pixel positions in the matrix of two-valued white pixels, at a pixel position or positions at each of which a colored two-valued white pixel is absent among the other of the first pixel positions and the second pixel positions in the matrix of two-valued white pixels, and outputting the set of two-valued white pixels forming the white base, which have been rearranged.