Any Morph that has altered the natrual color of the snake I would worry about the suns effects on it. ie. Albino, Snow, Anery, Ghost, Hypo and so on. These snakes are missing certian cells in their skin that may help prevent over exposure to the sun. The second issue I would worry about is more of a over heating then sunburn. Boas do not get a lot of direct natrual sunlight in nature. The live in heavily vegitated areas with much shade and cover. Further more, much of there range seldom exceeds 90 degrees but rather stays near the mid 80's all year long.
If you leave your snake out in the mid day sun on a 95 degree day with no cover it will quickly over heat.
I would recommend that you "take him for walks" in the early morning or evening when the heat is down a bit more and they would be active normally anyway.
I hope this helps
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Jim Hopkins "Hoppy"
Hopkins Holesale Herps
Hopfam1@aol.com