The colours that you choose for your horse's horse rugs will influence the amount of attention that they receive from insects, as will your horse's colouration. For instance, white horses get less attention from Marsh flies, or horse-flies, than darker-coloured horses. However, the fact that horse-flies are less likely to bother white horses may not necessarily relate to the brightness of their fur, or even its colour. It may be a function of horse-flies' attraction towards polarized light. Insects are extremely diverse. There is some evidence that other types of insects are attracted to brighter colours in general.
Rug Color and Insects
Insects can perceive colour in somewhat unpredictable ways. The shade of the color in question matters, as does its level of brightness. If you've worn brightly-coloured instead of light or neutral coloured clothing in an insect-infested area, you may have noticed that you got more attention from insects in the process. If you put your horse in a bright horse rug, he or she may experience the same thing. Bright colours tend to reflect much more light than they absorb, including ultraviolet radiation, which may explain why many insects like them.
The vision of insects is specifically geared toward the ultraviolet portion of the electromagnetic spectrum. Many flower species are bright yellow or white specifically because of their natural relationship with insects. Many horse rugs that are designed to be brightly-coloured, so you may have multiple factors to consider when choosing the colour of a horse rug. You may also have to select your horse rugs based on the specific insect threats that you are trying to avoid.
Insects respond differently to different colours. Interestingly, most insects cannot perceive the colour red, because their vision centers on different sections of the electromagnetic spectrum. If your horse wears a red horse rug, they may receive less attention from insects. While other methods of insect prevention mainly involve repelling them altogether, red horse rugs will simply make your horse less visible and appealing for insects. Unlike other methods of insect prevention, this method has no additional side-effects attached. Horse rugs that are dark red may be good choices for horse owners, since they won't reflect as much light as the brighter colours would, and they may be virtually invisible to many insects. There are two downsides. A dark red horse rug will attract more heat than a lighter coloured horse rug. The other main problem is that red will fade significantly faster than any other colour when exposed to the suns UV.
Lighter Green, Cream or Blue horse rugs are still less likely to attract the attention of insects than violet ones, even if dark red or orange horse rugs may be even better. As a horse owner, you may have different aesthetic preferences when it comes to horse rug colours. It comes down to finding a balance between lighter colours that reflect more light (hence stay cooler), colours that don't fade easily or show the dirt and that ultimately are aesthetically pleasing to look at.
Many horse owners have found success by using mesh horse rugs. If you live in an area with a great deal of insect infestation, mesh horse rugs may be the best option for you and your horse. Obviously, the problem becomes less important during the wintertime, and you can be more flexible on horse rug colours during the right seasons. Trying different horse rugs in different seasons will help you find the best option for you and your horse.