Question: Is it possible to have the color of the task bar change on the Gantt Chart based upon input in a cell.
 

Answer: Yes, here are the steps

1.  Within your project, Insert Flag 1, Flag 2 columns
2. Use the Tools, Customize, Fields, Options to rename Flag1 to Aqua, Flag 2 to Red

3. Ensure Aqua (Flag 1) is highlighted, right click, Customize, then click on Formula
4. Type in the following formula: IIf([Text1]="1",Yes,No)
5. Click on OK
6. Ensure Red (Flag 2) is highlighted, right click, Customize, then click on Formula
7. Type in the following formula: IIf([Text1]="2",Yes,No)
8. Click on OK
9. Right click on the Gantt chart portion of the screen and click on Bar Styles
10.Click on Task (under Name)
11.Click on Cut Row
12.Then Click on Paste Row 3 times

13.Click on second Task and rename to “Aqua Flag”. Rename third Task to “Red Flag”
14.Click on the Show For…Tasks column in the second Name
15.Click on the drop down, remove Name and Insert Flag 1
16.Click on Appearance for Flag1 and change the color to Aqua
17.Click on the next line down and remove Name and insert Flag 2
18.Click on Appearance for Flage2 and change the color to Red - click OK
 

19.As a final step, you may now hide the two Flag fields from your plan

Now when you input a 1 in Text1, the color of the task on the Gant chart will change to Aqua. If you input a 2, it will change to Red. No value, it will remain as the default Blue bar.

These are the basic steps for setting up an MS Project schedule to have the color formatting of the Gantt Chart task bars to change based upon values input in a cell.  Given this basic knowledge, you are now only limited by your own imagination and creativity on how to utilize this function of the tool.