The colours are a simulation: assume a given total rainfall over a given duration (say 350 mm in 24 hours), drainage works functioning normally, no buildings blocking the water, and let a hydraulic model compute the maximum depth class each cell reaches. It is not a forecast, not a record of any real flood, and not a statement about your house. Source: Water Resources Agency flood potential maps, third generation (August 2022 edition). Under the Flood Potential Data Disclosure Regulations it is for disaster-prevention reference only and may not serve as a basis for land-use control.
More: what a potential map is and is not, source and limitations, FAQ.
All run on one machine at home; the data tools use Taiwan government open data and state their limits.