Item Colors
When choosing your items, item color is an important but often overlooked aspect of the game. Become enlightened about the five item colors so that you can find harmony and prosperity in your games, and so you can choose the right balance of colors for your needs. If you are an ADC or APC main, this is pretty much required reading.
LET US BEGIN!
Blue items
Blue is by far the largest set of items, as well as the most diverse. Here you will find your staple mana items such as frozen heart, iceborne gauntlet, archangel's staff, manamune, and essence reaver. Unleash the power of winter with frozen mallet and rylai's crystal scepter. When you hear about people playing Blucian, Blukong, or Blue Ezreal, it is because they have found harmony using only blue items. Learn about the other blue items so that you can use their power as well.
Yellow items
Yellow items are all about the crits. You can get the ever-popular trinity force, infinity edge, or statikk shiv. Alternatively, counter the crits with randuin's omen or sunfire cape. A few hybrid champions can make use of nashor's tooth or guinsoo's rageblade. Try out the options here and you'll see what yellow items can do for you.
Red items
These items emphasize raw power. AD carries will find the bloodthirster, runaan's hurricane, and rapid firecannon helpful in crushing their opponents. AP carries can get their rabadon's deathcap. For you melee champions out there, you can get an edge over the competition with ravenous hydra, and AD champions of all kinds will enjoy the black cleaver. Use these items to dominate your foes.
Purple items
This is a smaller set of items which gives you the magic you need. Items like wit's end and maw of malmortius help shield the auto attackers from magic damage. For you AP carries, you'll gain a mystical edge over the enemy with luden's echo, rod of ages, and morellonomicon. Destroy tanks and become harder to kill with blade of the ruined king. For you tanks, you can unleash the power of the void with zz'rot portal. Remember: just because purple items are a smaller set doesn't mean you should overlook them.
Green items
This is by far the smallest set of items, and the least understood. They seem to be focused on survival. The most important members of this set are warmog's armor, spirit visage, hextech gunblade, and mercurial scimitar. If you can master their power, you will surely be able to find victory.
Conclusion
There are many items in League of Legends, and their colors create a complex but important relationship in the web of life and/or game balance. So far, nearly all items have been determined to have a color, and some items have more than one color! For example, blade of the ruined king could be considered to be either blue or purple. The background color of guardian angel hovers on the border between blue and green. Bear this in mind, and try not to argue too much about color with your peers. Someone may see a color in an item that you do not. Rather than reducing your discussions to petty accusations, have humility and seek wisdom. Only then will you become a true master of item colors.
Bows out