The Winged Fellowship Trust, which provides holidays for disabled people and carers and employs 350 staff, will become Vitalise on 1 November, with a new pink logo.
The charity says the change is "probably the biggest and most exciting change in our 41-year history" and has been "extremely well received by those in the charity".
But Paul Sample, who worked for The Winged Fellowship for four years until 1999 and now runs his own corporate communications business, says the charity's new name sounds "like some sort of sweet and sickly drink".
In a response to a letter the charity sent to thousands of supporters last week, Sample says he was putting forward his views because he cared about the work he did for the trust "over four happy years".
He claims elements of the stationery design looks like "a bloodstain" and he ridicules the use of "minor celebrity" patrons, who include Princess Alice, former newsreader Richard Baker and Lord Morris of Manchester.
Sample concedes in his letter that the new strapline is moving in the right direction: "You have dropped 'respite care', with all of the negative connotations that had. However, there is no mention of 'holidays' which, from the disabled person's point of view, is what you provide.
"It places you firmly in the care provider arena rather than the 'leisure' and 'holiday' sector. It still implies something provided 'for' disabled people, rather than valuing them as customers with consumer choices."
The charity wrote to donors, including Sample, last week explaining why it was abandoning the name adopted 41 years ago by founder Joan Brander, who died this year.
It said that 'winged' implied military or wildlife connotations and 'fellowship' had Christian overtones. "We believe that Vitalise, together with our new strapline 'Essential breaks for disabled people and carers' will position us as a more modern and visionary organisation," chairman Hugh Kemsley wrote in the letter.
Chief executive Pat Wallace said Sample's views contrasted to more than 100 other responses. He added that supporters had been kept informed about developments. He did, however, admit there were 'differing views' on the logo.
"This process has been running for two years and our founder was behind it, providing costs were kept to a minimum."
Sample admitted his comments were pungent. But he added: "If this starts a debate on how a charity should set about changing its image, then all well and good."