When you start learning Kanji, this will start to be more apparent as you will need to learn roots of words so that you can add the proper hiragana endings to the words. It gets even more crazy as you can use words from one part of speach as another part of speach by just changing the ending.
赤く・あかく is actually the adverbial form used to link it to verbs and other adjectives :)
The final い of an i-adjective is dropped and く is added,
木の葉が赤くなった "The leaves of the tree have become red" ('red' is modifying the verb 'to become')
赤く染める・あかくそめる is "to dye red", which tends to be a common phrase from some violent anime characters. Akaya from Prince of Tennis comes to mind, "I'll dye you red!" also has a character song called 赤く染める月 "Red-tinted moon"