In Colorado, and most states for that matter, there is not a separate legal entity type called 'PLLC' (professional limited liability company). See list of entity types from Colorado Secretary of State's office. Professionals form a standard LLC; however, the rules of the applicable state professional organization (bar association, medical board, board of accountancy, et cetera) mandate that the LLC carrying on a profession operate under certain additional rules not applicable to normal LLCs. These rules are not found in the state corporate code (i.e., Colorado Stat. § 7-90, et alia) but, rather, state laws specifically governing the profession in question.
The case of accountants, the application Colorado law is § 12-2-117. Of particular interest on the issue of liability is paragraph (3)(c) of this statute:
(c) All partners, shareholders of the corporation, or members of the limited liability company shall be jointly and severally liable for all acts, errors, and omissions of the employees of the partnership, corporation, or limited liability company except during periods of time when the partnership, corporation, or limited liability company maintains in good standing professional liability insurance, or designated or segregated moneys in lieu of such professional liability insurance, which meets the standards set forth in subparagraphs (I) to (V) of this paragraph (c) ... .(Emphasis added.) What I take away from the above is that a member of an accounting LLC in Colorado is afforded the standard liability protection of LLCs EXCEPT for "errors and omissions of employees", for which they are personally liable. The Colorado law contains a further exception to the exception holding that members of accounting LLCs avoid personal liability for the errors and omissions of their employees by maintaining insurance that meets the standards set forth in the statute.
This earlier blog post discusses PLLCs further. I believe this form is used to qualify your PLLC with the Colorado Board of Accountancy after its formation. Further, MedLawPlus.com® sells an operating agreement specifically designed for PLLCs.