On its way to Verizon images is in advertisement so may be expected or possible color variation further models and series.
According to market based leak news blue and pink would be two further variations would be introduced.
HTC ONE was launched in blue color series, so same possibility with m8 series according to news and advertisement in picture is expected with m8 series.
Pink is the new variation which they are adding with m8 series and it would be a good combination with this color series of m8.
The three color variation based series will be in market in few expected days and market availability would be according to plan of distribution of series as per marketing strategy of HTC.
The response of M8 Sales and Marketing and Distribution is quit satisfactory, at least in United States of America, if the company or brand is going to add more color with possible series in same model then it would be a fortune making policy with this model around the world specially in United States.The gunmetal grey model is the standard handset for one m8 review and color variants are expected right now as per market leak news and market based news of brand and its variation