Colored runway multipliers can only be earned in Odyssey and Rescue modes. This achievement requires you to get a multiplier of 50. Successively landing the same color ships in a row will add to the multiplier. Landing a ship of a different color from the current multiplier or crashing any ships will reset the multiplier. So, to earn this achievement, you need to land 50 ships of the same color in a row without landing another color, or crashing any ships.
This achievement is most easily attempted in Infinity mode. Ships of like color tend to spawn together for extended periods of time. You should attempt this with either large green or large yellow ships, which spawn smaller ships, as well as the yellow snake-like ships (each ship in those chains count towards the 50). Finally, the cargo ships which drop off 10+ ships of the same color can be useful as well.
This will take a little bit of luck. If a ship spawns of the wrong color, just stall it around the screen and don't land it. This achievement could take a while if you don't have the luck.