Printer prints wrong color

Hi
A friend of mine has a canon printer, she thinks the model is BJC24, it has a small cartridge that 2 ink tanks sit in,one black and the other color. A couple of weeks ago she replaced the cartridge and recieved 2 ink tanks with the replacement unit.She replaced the unit because the printer would not print at all, after she had reinstalled it and the appropriate drivers a number of times. At first the replacement worked beautifully but now it has decided to print in whatever color it wants to and changes color without any user input at all. She has an old computer and still runs windows 95. Has anyone had or seen a similar problem? Software or Hardware issue?