What does a blood clot look like on forearm. a bruise-like circle of about a 1/2 inch just showed up; yesterday it was brown and today it is red. ?

Varies: Blood clots can produce different presenting symptoms. If it is in the artery, it can cause dramatic pain and even turn the limb blue/black if it blocks important circulation to the rest of the arm. If in the vein, it will lead to swelling in the limb. If you have a bruise, it is likely a small bursted vessel. You may want to consider an insect bite too (spider?) and it may be infected.