Note as @Nexus mentioned below, the FormatConditions
collection will only accept 3 conditions. But you were aiming for 4 conditions. Unless you can consolidate those into only 3, you won't be able to use Access' conditional formatting feature for this.
With the form in Design View, right-click the text box and choose "Conditional Formatting ..." from the context menu.
Select "Field Value Is" from the drop-down under Condition 1, "between" in the second drop-down, and enter your start (0) and end (25) range values in the next 2 boxes. Choose red from the Font/Fore Color drop-down.
Click the "Add >>" button to add another condition (Condition 2). Set the values for that condition: 26; 50; and yellow.
Repeat for the remaining conditions.
Here's a screen capture of your first 2 conditions applied to a text box. (I chose light grey for the background color so the foreground colors would be more distinct in format preview area.)