Sometimes the pink belly will indicate an upcoming shed. Our 7' female gets real hissy if she's disturbed while in blue.
Head to the local WalMart and get a human heating pad (without auto-shut-off) for under the cage, set on low and monitor the temps. Use a couple of pencils or chopsticks to raise the bootom a little to allow for airflow so the pad does not overheat. Pads are around $10-$12 usually, much cheaper than the 'reptile mats' that will need a rheostat as well.
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Good luck.