I think you are asking about cryptic coloration, which insects and other mostly small living things use to blend in with their environment.
If the front two pairs of legs of the spider you saw were much longer than the rear legs, it may well have been a crab spider, such as JeremyHussell mentions.
Crab spiders do not use webs to catch prey. Instead they blend in and hide. When a prey insect lands on the flower where they are hiding, they use the long front legs to capture it. Ambush bugs have a similar strategy.
If you Google cryptic coloration you will find some amazing examples of animals that blend in.
BTW, if you are interested in plants that depend on certain insects, iNat has a number of pollinator projects.