Global tablet shipments fell 28 percent to 7.2 million units in the first quarter, compared to fourth quarter sales in 2010, according to market intelligence firm IDC.

Sales of ereaders, which IDC counts separately from tablets (rightly so), also fell for the quarter. But IDC notes that for the first time ever, Barnes & Noble’s Nook Color — an ereader with a healthy dose of tablet-like functionality — has toppled Amazon’s Kindle as the lead device in the category.

The tablet sales dip reflects seasonal trends that normally affect more mature consumer electronics categories, IDC said, which hints that consumer demand for tablets may be far less than the hype the category has built up. That’s bad news for every tablet manufacturer except Apple, whose iPad (now the iPad 2) continues the dominate the category.

Despite the slower tablet sales, IDC has increased its tablet shipment forecast to 53.5 million units this year, up from a 50.4 million unit projection. Android tablet sales now account for 34 percent of the total, a jump of 8.2 points over last quarter.

Ereader shipments fell from the holiday rush to 3.3 million units, but still saw a 105 percent increase compared to last year. As for the Nook Color’s success, IDC points to Amazon’s lack of a color ereader as a reason for losing the lead sales spot. Rumors remain strong that Amazon will announce its own tablet devices in a few months, and I would imagine at least one will be an inexpensive Kindle-branded tablet/ereader device like the Nook Color.

The 7-inch Nook Color retails for $250 and features a multitouch screen that functions just like a tablet. Barnes & Noble recently updated the Nook Color to support a limited selection of apps, a Flash-capable web browser, and more. For consumers who can’t afford a $499 iPad, the Nook Color seems like a no-brainer compromise.

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