The way to fix this is to manually edit the configurations files:

/usr/share/themes/Ambiance/gtk-3.0/settings.ini
/usr/share/themes/Ambiance/gtk-3.0/gtk.css
/usr/share/themes/Ambiance/gtk-2.0/gtkrc

And to replace the values of tooltip_bg_color and tooltip_fg_color.

To make it easier I created a script that does that automatically, it can be downloaded here. To run the script, open a terminal, go to the download directory and run:

chmod +x tooltipfix
sudo ./tooltipfix themeName

Where themeName is an optional argument to specify the target theme (default is “Ambiance”).

V. Pillac, M. Gendreau, C. Guéret, A. Medaglia
A review of dynamic vehicle routing problems
Technical Report CIRRELT-2011-62, Centre interuniversitaire de recherche sur les réseaux d’enterprise, la logistique et le transport (CIRRELT), Montreal, Canada, 2011

Abstract

A number of technological advances have led to a renewed interest on dynamic vehicle routing problems. This survey classifies routing problems from the perspective of information quality and evolution. After presenting a general description of dynamic routing, we introduce the notion of degree of dynamism, and present a comprehensive review of applications and solution methods for dynamic vehicle routing problems.

V. Pillac, A. Medaglia, C. Guéret
An event-driven optimization framework for dynamic vehicle routing
Technical Report 11/2/AUTO, Ecole des Mines de Nantes, France, 2011

Abstract

The real-time operation of a fleet of vehicles introduces challenging optimization problems researches in a wide range of applications, thus, it is appealing to both academia and practitioners in industry. In this work we focus on dynamic vehicle routing problems and present an event-driven framework that can anticipate unknown changes in the problem information. The proposed framework is intrinsically parallelized to take advantage of modern multi-core and multi-threaded computing architectures. It is also designed to be easily embeddable in decision support systems that cope with a wide range of contexts and side constraints. We illustrate the flexibility of the framework by showing how it can be adapted to tackle the dynamic vehicle routing problem with stochastic demands. Computational results show that while our approach is competitive against state-of-the art algorithms, it still ensures greater reactivity and requires less assumptions (e.g., demand distributions).

But first what is the effect of the server flag? In a nutshell it tells the JVM to spend more time on the optimization of the fragments of codes that are most often used (hotspots). It  leads to better performance at the price of a higher overhead at startup.

Therefore, when benchmarking an algorithm it would seem interesting to switch this on to reduce running times.

I tried it on my own benchmarks (on an Ubuntu 64bits machine) and found out that there were no significant change in runtime, while other people were talking of a reduction of 20 to 40%. It turned out that depending on the machine and operating system, the JVM would automatically turn this option on or off: in fact in any recent computer with an OS different from windows 32bits it will be turned on by default.

Please note that you will need to install the JDK to use the server mode on a 32bits windows machine.

More information can be found in the Java HotSpot FAQ:

What’s the difference between the -client and -server systems?
These two systems are different binaries. They are essentially two different compilers (JITs)interfacing to the same runtime system. The client system is optimal for applications which need fast startup times or small footprints, the server system is optimal for applications where the overall performance is most important. In general the client system is better suited for interactive applications such as GUIs. Some of the other differences include the compilation policy,heap defaults, and inlining policy.

Where do I get the server and client systems?
Client and server systems are both downloaded with the 32-bit Solaris and Linux downloads. For 32-bit Windows, if you download the JRE, you get only the client, you’ll need to download the SDK to get both systems.

For 64-bit, only the server system is included. On Solaris, the 64-bit JRE is an overlay on top of the 32-bit distribution. However, on Linux and Windows, it’s a completely separate distribution.

I would like java to default to -server. I have a lot of scripts which I cannot change (or do not want to change). Is there any way to do this?
Since Java SE 5.0, with the exception of 32-bit Windows, the server VM will automatically be selected on server-class machines.

The definition of a server-class machine can be found here:

In the J2SE platform version 5.0 a class of machine referred to as a server-class machine has been defined as a machine with

• 2 or more physical processors
• 2 or more Gbytes of physical memory

On server-class machines by default the following are selected.

• Throughput garbage collector
• Heap sizes
• Initial heap size of 1/64 of physical memory up to 1Gbyte
• Maximum heap size of ¼ of physical memory up to 1Gbyte
•     Server runtime compiler

V. Pillac, C. Guéret, A. Medaglia
On the Technician Routing and Scheduling Problem
Proceedings of the 9th Metaheuristics International Conference (MIC 2011), 675 – 678, Udine (Italy).

Some pictures of the host city of Udine: