PICTURE this: an overseas client has arrived in the factory to place orders for next year. He likes the patterns of some materials but not the chosen colours, and wants to see variations - now. A major problem not so long ago, this can now be quickly solved using a computer which reproduces the selected pattern on the screen in an almost infinite range of colours, allowing the customer to choose those he prefers. As patterns look different depending on whether they are laid flat on the cutter's table or draped over a body, the computer screen can also show the material as it will look on a human being, either as a tight-fitting swim suit or a loosely draped dress. This use of computer-aided design and manufacturing (CAD/CAM) is common in Hong Kong factories. The textile industry makes considerable use of computers to ensure maximum efficiency in the use of materials, as well as flexibility and productivity. ''There is a good market for CAD systems in Hong Kong, but an even better one in China,'' said Bruce Cheng, executive director of Global Gartech Services (GGS), which imports these systems from Europe to sell in Asia. Among other things, CAD is used in Hong Kong for fashion design, pattern creation, grading and marking, and fabric cutting. Computerised fashion design can help speed up the design process by creating sketches to build up styling. It also allows the designers to play with colours. Alternatively, pictures from a camera can be transferred to the screen to be used as models. GGS imports a Spanish Ivestronica machine, which provides computerised pattern creating, grading and marking, and an automatic cutting system. This cutting system determines how patterns will be cut from a roll of cloth to avoid wastage. Computer planned cutting is commonly used in the leather industry for the same reason. Grading is necessary after the sample has been approved to adjust pattern sizes to meet different people's sizes. Computerisation limits room for error and speeds up the process. A CST machine from Germany uses a colour scanning technique to provide colour separation for the printing industry. The Alohatex 2000 from France offers printing design through a colour separation system which is connected to a laser engraving machine.