A slot machine 10 has three rotatable reels 12 carrying symbols 14 which are controlled by stepper motors and are arranged to pay prizes on the occurrence of a predetermined symbol or combination of symbols. A jackpot prize is paid on the occurrence of three 7s on the win line. The 7s are against a clear background and when three 7s appear on the display the display colour may change to three red 7s, three blue 7s, three white 7s or three 7s of mixed colour. If the three 7s all change to a red colour, the jackpot prize is paid, otherwise a lesser prize is paid. The colouring of the 7 occurs by backlighting the 7s in the reels by means of coloured light bulbs or similar means. The presence of the above feature on a gaming machine allows that gaming machine to pay a jackpot which is several times greater than would normally be paid. For example if each 7 has all equal chance of becoming white, blue or red, then the chance of all three reels turning red is 1 in 27 and therefore a jackpot prize of approximately 27 times greater than all identical gaming machine without the feature of the present invention can be paid.