Nothing to see here.
The Landscaping Department of Urban and Rural Construction had this to say about the choice to paint the grass:
[…] colored nutrient fluid that contains trace amounts of fertilizer that can improve the grass's frost-resistance and appearance. Nutrition deficiency makes the grass turn yellow in winter and [if not treated] the grass can wither by summer. Using the greening agent is a kind of supplement for the grass's nutrition, and this greening agent poses no danger to plants, people, the soil, or the environment. From its use from 2008 to today, no problems have ever occurred.