One wonderful thing about decorating is that you can have a wide variety of texture, design and colour to create your own personalised look. Not only is having a non-matching cushion okay, it's actually more interesting and aesthetically pleasing. Imagine a room with everything the same tone of beige. It would be both monotonous and boring.
Varying colour choices
Bringing a variety of colours into your décor doesn't have to look like the circus is back in town either. You know the look, bright reds, brilliant yellows all against a stark white, blue or brilliant orange background. Busy flowers and geometrics with plaids and clashing patterns everywhere. Neither the garish over-embellished look, nor the sterile single colour look are attractive. You need variety, but with complimentary colours and designs.
Don't get the wrong idea, a monochromatic colour scheme can be attractive. However, even monochromatic colour schemes use variety, albeit a variety of the same colour or undertone. Many times these use rich deep tones and ultra light ones of the same colour. You can use complementary colour schemes with contrasting colours, too. Brilliant colours can also bring a lot of cheer to the room as long as the colours are chosen carefully and used skilfully.
Complementary colour schemes
Complementary colour schemes are those right across from each other on the colour wheel, such as yellow and purple or red and green. Other colour combinations can be grouping warm and cool colours. Often people look to the largest pattern in the space, such as a carpet, and use the colours in it for their colour scheme. You can choose colours for cushions based on similar colours. Just look at the colour of the sofa or your room's colour scheme, find colours next to it on the colour wheel and you have an analogous colour scheme.
An example is blue and green, both of which are cool colours that provide relaxation. If you're looking for cushions for your sofa, consider how your room feels. If it feels to formal, consider using softer colours to tone down the room. Add lighter tones to brighten it. For a black and white room, a few coloured cushions can add just the right splash of colour to set off the entire room and make it more inviting.
Mix and match your cushions, use a variety of different textured fabrics and sizes to create an interesting room that suits the style of your home and your decorating motif.