A rumor earlier this month claimed that Microsoft was working on a substantial "Blue" update for Windows Phone and Windows 8, and confirmation apparently surfaced.

The Blue update allegedly includes tweaks to improve user experience and potentially help bridge the gap between development platforms. Microsoft did not say anything officially about the Blue update, but new job listings now contain references to Windows Phone Blue and Windows Blue.

ZDNet uncovered a Feb. 15 job listing on the Microsoft Careers site. The ad disappeared in the meantime, but the job was for a software development engineer in test and mentions "Windows Blue." According to the posting, the Core Experience team in Windows Sustained Engineering (WinSE) is working on making improvements to several areas of the operating system.

"We're looking for an excellent, experienced SDET to join the Core Experience team in Windows Sustained Engineering (WinSE). The Core Experience features are the centerpiece of the new Windows UI, representing most of what customers touch and see in the OS, including: the start screen; application lifecycle; windowing; and personalization. Windows Blue promises to build and improve on these aspects of the OS, enhancing ease of use and the overall user experience on devices and PCs worldwide," read the job listing.

According to ZDNet's sources, Blue is the codename for Microsoft's next set of Windows-related OS and services updates. Microsoft will push a Blue update to Windows 8, Windows Server 2012, Windows Phone 8 and Windows Services such as SkyDrive and Hotmail. Moreover, Microsoft is betting on Blue to adopt a more rapid update pace.

When it comes to Windows and Windows Phone, Blue should include several new features, and even new programming interfaces to create a more unified front for the different flavors of Windows from and app model/ development model point of view. As the job listing reveals, Blue will not only bring updates to Windows internals, but also to the user interface and experience.

Microsoft officials have declined to offer any comments on Blue, and it remains uncertain at this point whether the update pack will be officially called Blue when it's released. It may come as a refresh to Windows 8 rather than a whole new version of Windows.

Meanwhile, a Windows Phone Blue job reference brings more details about Microsoft's plans in this area.

"The Excel Office Mobile team is looking for a seasoned development lead who is willing to re-imagine the Excel experiences for the next versions of Windows Phone. Our Vision is to make Excel Mobile on Windows Phone the undisputed leader for visualizing and working with spreadsheets on a phone. The Excel Mobile team will deliver a compelling new Windows Phone version of Excel that is touch-optimized and targeted for the phone form factor," reads the job posting.

"As a development lead you will hire and manage a team of top-notch developers, be personally involved in designing and coding features, and work closely with PM and Test counterparts across multiple orgs to help realize the vision of building high quality excel app for Windows Phone Blue. In partnership with the Excel MX, Data Visualization and Excel Web Services team your team will be responsible to develop a common code enabling us to build a mobile app which will (1) allow users to have a consistent experience with spreadsheets across Web, Slate and Phone end while leveraging the power of the cloud (Excel Web Services, Office Client Services, SkyDrive and O365).

The intriguing "Excel MX" mention likely refers to a fully touch-optimized and Metro Style/ Windows Store version of Excel that is yet to debut.