Remove & discard outer leaves & stalks of cauliflower, leaving head whole.
Place cauliflower in a large saucepan; add water & salt. Bring to boil;cover, reduce heat to medium, & cook 10 to 12 minutes or until tender. Drain well. Cut cauliflower into 6 portions; place on a serving platter, cover & keep warm.
Saute onion, green pepper, & red pepper in 1 Tbs. melted butter in a skillet until tender; drain well & set aside.
Melt 3 Tbs. butter in skillet over low heat; add flour, stirring until smooth. Cook 1 minute, stirring constantly. Gradually add milk; cook over medium heat, stirring constantly until thickened & bubbly. Add cheese, dry mustard, & white pepper; stirring until cheese melts. Remove from heat; stir in reserved onion mixture.
Spoon sauce over cauliflower. Sprinkle with crumbled bacon & toasted almonds. Serve immediately.