Generally, hair grows an average of ½" to ¾ " per month. It's important to consider that longer hair can grow without interrupting the style or features of your cut, but ½" of growth can cause problems for shorter hair styles. It is best to keep your hair trimmed so you never look like you need a hair cut.
In regards to color or highlight touch up, "obvious roots" are never in style. We recommend retouches based on growth, style, and color of your hair in comparison to your natural color. A good rule of thumb is to color every 3-6 weeks. On a side note; your hair will grow faster if you get it trimmed. It''s best to keep a crisp end to your hair when you are trying to let it grow.