It all gets messier when you account for the atmospheric composition. Water Vapor reflects some % of light away and allows some % of IR radiation through. The cloud composition of Venus differs (it's Mainly CO2) a well known Greenhouse gas. So Reflection is high but the CO2 traps whatever heat reaches to the ground and doesn't let it out, causing the heat buildup observed today.
On a side note, check these reprocessed Venus images from the Venera legacy, there are some fantastic cleanup and sharpening of the original data made by Don Mitchell http://www.mentallandscape.com/V_DigitalImages.htm
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