This tip came to me from Lynn Oburg, one of Crooked Arm's developers. We were able to help our customer using this innovative technique that wouldn't have been nearly as elegant before FileMaker Pro 9.

Figure 1: Conditional formatting -- Until there's unconditional formatting, you'll have to use this.

Figure 2: Choose wisely -- Use your conditional common sense to pick a pleasing palette.

Figure 3: A clue! -- The required fields are obvious now. If you see yellow, you aren't finished yet.
Our customer takes dozens of telephone orders per day and must gather a lot of information for each order. To make matters worse, the required information changes based on a number of factors. Traditionally, we would have used validations on each field to display an error message when a user left a required field empty. Unfortunately, field validation isn't without its own problems, the primary offender being FileMaker Pro's default error message which can be confusing. We've also built "shadow" fields that let users fill out the form unhindered by validation. When the form is complete, the user clicks on a Save button and we use a script to validate the entire form at once. This approach provides a better user experience, but adds hours of development time. Lynn's approach is to use conditional formatting, a feature new to FileMaker Pro 9.
Conditional formatting simply changes the way fields and some other layout objects appear based on criteria you specify. Let's start with the required fields. Open any database in FileMaker Pro 9 and enter Layout mode. Select any field and choose "Conditional…" from the Format menu (figure 1). In the Conditional Formatting dialog that appears (figure 2), click on the Add button and set the condition pop-up menus to "Value is" and "empty."
Under format, select the "Fill Color" box. Choose a fill color that is distinct enough to call attention to itself among the other colors on your layout. You should also be careful to select a color that contrasts well with the text color in that field. White text on a yellow background, for example, will cause some nasty headaches. Bright red on a bright blue background, when stared at, will start to look like one of those anime cartoons that cause seizures. Refer to the example provided in the Conditional Formatting dialog to ensure you won't be the source of suffering … for this, anyway.
Click on OK and enter Browse mode to see your handiwork. When the field is empty, it should display the colored background. After you enter a value, however, the background reverts to the default. Now, when creating a new record, users can easily perceive which fields are required (figure 3).