Thick and blue, tried and true. Thin or crispy, way too risky. That's the old saying, and it's a good one. Take a hard look at the ice before you leap. Clear blue ice is the strongest, and it still takes three inches to safely hold a single person, and five to six inches to safely hold a group of people or a snowmobile.
Ice is inconsistent.
Milky, honeycombed ice that has air bubbles or snow crystals trapped in it is much weaker and less trustworthy than clear blue ice. Water currents under the ice or springs can create weaker spots that will hold up people but not anything heavier. Snow cover complicates things with ice. Not only does it keep you from visually checking the ice for inconsistencies, it also insulates and inhibits ice formation. So be extra careful before venturing out onto a snow-covered pond or lake.