The ultrasound window can look different for every sensor. The optical properties of the window are not a controlled parameter which means the color and homogeneity of the window can vary.
A truly damaged ultrasound window can be seen by scratches, indentations or water ingress. In such cases, replacement is advised. The majority of ultrasound transducer are damaged via exterior mechanical influences: rocks, sharp objects, abrasion or (temperature) shocks.