For the same reason that some things taste good or bad, or smell good or bad - our biological background establishes preferences for things that help our survival.

For instance, we have a taste for fatty, sugary, salty foods. That keeps us alive, as opposed to eating dirt. Fatty, sugary and salty foods have the high-energy nutritious material we need.

Discover Magazine - Why Fat Tastes So Good|http://discovermagazine.com/2006/feb/why-fat-tastes-so-good

Most of us find dung and urine repulsive smelling/tasting. That is good - they are a source of disease, so we are better off separating ourselves from it as much as possible. Through our evolution, those humans who weren't as repulsed by feces were more likely to die from fatal diseases... so over time we started to find it repulsive.

Sight is another sense, like smell and touch, and "tasty" can be thought of as "beautiful" for taste. If one pays attention, beautiful things tend be colorful things, as opposed to a bland white. Rich blue reminds us of bountiful water - and therefore, life. Rich green reminds us of woods/plants - and therefore, food. Rich reds, purples and yellow can remind us of fruits and vegetables, that evolved to take advantage of animals' attraction to various colors.

We like bright, rich and lush. We don't need God or magic to explain this.