In 1989, ITV tried to make a unified brand for ITV, rather than the regional stations like before. A unified brand would have been cheaper and easier to market. Idents were created as well, but they weren't mandatory, and some even contained errors in the regional symbol on the V cone (Granada's didn't have the line joining the G to the arrow, and Anglia's had some colours mixed up) so several companies (Granada, Anglia, TVS, TSW, Ulster) turned them down. Grampian was the only region to keep the ident for it's full run - they only replaced it when ITV's logo was changed.
On October 5th 1998, ITV released a new logo, to make the channel seem less 'highbrow', and to try and make another unified brand across the UK. Many more companies adopted the idents this time round, but quite a few still refused. The font is a modified 'OCR-B', with an edit to the t.
In 2002, another set of idents were released, which featured celebrities acting casually in a blue and yellow set. This time, all the regions took them, although Scottish, Grampian and UTV used their own brands instead of ITV1. In 2004, ITV network centre became essentially redundant, although it still exists, as Carlton and Granada merged to form ITV plc.
Note: ITV4 used this logo from launch in 2005, but the other ITV channels didn't adopt it until January 2006, when it become the official corporate logo.
On 15 November 2012, it was announced that as part of a major rebranding, ITV1 will be renamed to its original name, ITV. In addition to this, ITV will have a new colour-changing logo stylised as handwriting, that changes colour depending on the programming it is used on. The overhaul is linked to ITV's attempt to cut costs, curb debts and reduce the company's reliance on advertising. This overhaul of their brand affected all ITV channels and online services on 14 January 2013.