Strong alkalis are typically colorless or white in their solid form. However, their solutions can be colorless or slightly yellowish depending on the specific alkali and its concentration.

Here's why:

* Colorless: Many common strong alkalis, like sodium hydroxide (NaOH) and potassium hydroxide (KOH), are colorless when dissolved in water. This is because they don't absorb visible light.

* Slightly Yellowish: Some strong alkalis, especially when concentrated, can appear slightly yellowish. This is due to the formation of small amounts of colored compounds, like peroxides, as they react with air and water.

Important Note: While the color of an alkali can be a helpful indicator, it's essential to remember that the appearance alone doesn't determine its strength. Always handle alkalis with caution, as they can be highly corrosive and dangerous.