Resizing is controlled in the LR Export Dialogue (brought up by hitting the "Export" Button at the bottom of the Left hand column, Ctrl/Shift/E, or several other methods), there are nine sections in the dialogue and image sizing is the fifth. If you tick the "Resize to Fit" box, you are then offered a choice of options, "Length and Width", "Dimensions", Long or Short edge, or even Megapixels. In the various dimension options you have the choice of specifying the dimensions in pixels, or lengths (both inches or cm). There is also an option to set the Resolution (in either Px/inch or Px/cm), to be used for both calculation the number of pixels when the size is defined by the lengths, as well as in determining the exact amount of output sharpening the will be applied.
As Tony said it is a good idea to have a read up regarding the most suitable export options for the use that you will be making of the images. The issues that you have with the colour sound like they may be due to having an unsuitable colour space being applied to the output file, if in doubt be sure to have sRGB selected.